This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons folder. You should end up with a directory structure similar to below:

• steamapps
  • common
    • garrysmod
      • garrysmod
        • addons
          • Huge Stool Pack!!! <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• Huge Stool Pack!!!/
  • Huge tool pack/
    • Advanced Duplicator/
      • Adv Duplicator/
        • data/
          • adv_duplicator/
            • biglandmine.txt
        • info.txt
        • lua/
          • autorun/
            • Beam_NetVars.lua
            • client/
              • cl_advdupe.lua
            • RDBeamLib.lua
            • Serialiser.lua
            • server/
              • AdvDupe.lua
            • shared/
              • dupeshare.lua
          • effects/
            • PasteBeam/
              • init.lua
          • entities/
            • Beam_Drawer/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_adv_dupe_paster/
              • cl_init.lua
              • init.lua
              • shared.lua
          • weapons/
            • gmod_tool/
              • stools/
                • adv_duplicator.lua
        • settings/
          • controls/
            • adv_duplicator.txt
    • Bridge Stool/
      • BridgeTool/
        • info.txt
        • lua/
          • entities/
            • bridgepiece/
              • cl_init.lua
              • cl_init.lua.bak
              • init.lua
              • init.lua.bak
              • shared.lua
              • shared.lua.bak
          • weapons/
            • gmod_tool/
              • stools/
                • bridgetool.lua
                • bridgetool.lua.bak
    • Conna's Stool Pack!/
      • Conna's Tools Pack/
        • info.txt
        • lua/
          • autorun/
            • ContraptionSaver.lua
          • entities/
            • gmod_commandbox/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_fan/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_perimeterturret/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_perimeterturret_rocket/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_pressurepad/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_radio/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_sensor/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_timer/
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_toggleablehoverball/
              • cl_init.lua
              • init.lua
              • shared.lua
          • PerimeterTurrets/
            • Laser.lua
            • Rocket.lua
            • Shotgun.lua
            • SMG.lua
          • weapons/
            • gmod_tool/
              • stools/
                • breakableprops.lua
                • cloaking.lua
                • commandbox.lua
                • constraintbreaker.lua
                • contraptionsaver.lua
                • fadingdoor.lua
                • fan.lua
                • perimeterturret.lua
                • positionswitcher.lua
                • pressurepad.lua
                • rotator.lua
                • sensor.lua
                • timer.lua
                • toggleablehoverballs.lua
    • Cratemaker Stool/
      • CrateMaker/
        • info.txt
        • lua/
          • entities/
            • m_crate/
              • cl_init.lua
              • init.lua
              • shared.lua
          • weapons/
            • gmod_tool/
              • stools/
                • cratemaker.lua
    • Door Stool/
      • DoorSTool/
        • info.txt
        • lua/
          • weapons/
            • gmod_tool/
              • stools/
                • door.lua
    • Force Dynamite/
      • forcedynamite/
        • info.txt
        • lua/
          • entities/
            • gmod_forcedynamite/
              • cl_init.lua
              • cl_init.tag
              • init.lua
              • init.tag
              • shared.lua
              • shared.tag
          • weapons/
            • gmod_tool/
              • stools/
                • forcedynamite.lua
                • forcedynamite.tag
    • Headcrab Canisters Stool/
      • headcrab canisters tool/
        • info.txt
        • lua/
          • weapons/
            • gmod_tool/
              • stools/
                • headcrab_canisters.lua
        • materials/
          • VGUI/
            • headcrabs/
              • headcrab_fast.vmt
              • headcrab_fast.vtf
              • headcrab_normal.vmt
              • headcrab_normal.vtf
              • headcrab_poison.vmt
              • headcrab_poison.vtf
        • settings/
          • controls/
            • headcrab_canisters.txt
    • Laser Stool v1.2/
      • Laser STOOL/
        • info.txt
        • lua/
          • entities/
            • madjawa_laser/
              • cl_init.lua
              • init.lua
              • shared.lua
          • weapons/
            • gmod_tool/
              • stools/
                • laser.lua
      • Readme.txt
    • Sensor Stool/
      • Sensor Tool/
        • info.txt
        • lua/
          • entities/
            • gmod_sensor/
              • cl_init.lua
              • init.lua
              • shared.lua
          • weapons/
            • gmod_tool/
              • stools/
                • sensor.lua
    • Smart Freezer/
      • Smartfreezer/
        • info.txt
        • lua/
          • weapons/
            • gmod_tool/
              • stools/
                • freezer.lua
    • Smart Welder v2.1/
      • smart_welding/
        • info.txt
        • lua/
          • weapons/
            • gmod_tool/
              • stools/
                • smartwelder.lua
    • The Famous Stacker!!!/
      • READE ME.txt
      • Stacker/
        • info.txt
        • lua/
          • weapons/
            • gmod_tool/
              • stools/
                • ol_stacker.lua
    • Weight Stool/
      • WeightSTool/
        • info.txt
        • lua/
          • weapons/
            • gmod_tool/
              • stools/
                • weight.lua
    • Wing Stool v1.1/
      • wing stool v1-1/
        • gamemodes/
          • sandbox/
            • entities/
              • weapons/
                • gmod_tool/
                  • stools/
                    • wing.lua
    • Wiremod!!!/
      • wire/
        • .svn/
          • entries
          • format
          • prop-base
          • props
          • text-base/
            • info.txt.svn-base
          • tmp/
            • prop-base
            • props
            • text-base
        • cfg/
          • .svn/
            • entries
            • format
            • prop-base
            • props
            • text-base/
              • vkeyboard.cfg.svn-base
            • tmp/
              • prop-base
              • props
              • text-base
          • vkeyboard.cfg
        • data/
          • .svn/
            • entries
            • format
            • prop-base
            • props
            • text-base
            • tmp/
              • prop-base
              • props
              • text-base
          • CPUChip/
            • .svn/
              • entries
              • format
              • prop-base
              • props
              • text-base/
                • amount.txt.svn-base
                • bball.txt.svn-base
                • digicam.txt.svn-base
                • elev.txt.svn-base
                • helloworld.txt.svn-base
                • screentest.txt.svn-base
                • screentest2.txt.svn-base
                • speedtest.txt.svn-base
              • tmp/
                • prop-base
                • props
                • text-base
            • amount.txt
            • bball.txt
            • digicam.txt
            • elev.txt
            • helloworld.txt
            • screentest.txt
            • screentest2.txt
            • speedtest.txt
          • ExpressionGate/
            • .svn/
              • entries
              • format
              • prop-base
              • props
              • text-base
              • tmp/
                • prop-base
                • props
                • text-base
            • examples/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • advsmoother.txt.svn-base
                  • convert.txt.svn-base
                  • helloworld.txt.svn-base
                  • stopwatch.txt.svn-base
                  • uptime.txt.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • advsmoother.txt
              • convert.txt
              • duplex/
                • .svn/
                  • entries
                  • format
                  • prop-base
                  • props
                  • text-base/
                    • duplexer.txt.svn-base
                    • merger.txt.svn-base
                    • splitter.txt.svn-base
                  • tmp/
                    • prop-base
                    • props
                    • text-base
                • duplexer.txt
                • merger.txt
                • splitter.txt
              • helloworld.txt
              • outdated/
                • .svn/
                  • entries
                  • format
                  • prop-base
                  • props
                  • text-base/
                    • clock.txt.svn-base
                    • conditional.txt.svn-base
                    • interface.txt.svn-base
                    • latch.txt.svn-base
                    • vehicle.txt.svn-base
                  • tmp/
                    • prop-base
                    • props
                    • text-base
                • clock.txt
                • conditional.txt
                • interface.txt
                • latch.txt
                • vehicle.txt
              • stopwatch.txt
              • uptime.txt
          • WireModelPacks/
            • .svn/
              • entries
              • format
              • prop-base
              • props
              • text-base/
                • default.txt.svn-base
              • tmp/
                • prop-base
                • props
                • text-base
            • default.txt
        • info.txt
        • lua/
          • .svn/
            • entries
            • format
            • prop-base
            • props
            • text-base
            • tmp/
              • prop-base
              • props
              • text-base
          • autorun/
            • .svn/
              • entries
              • format
              • prop-base
              • props
              • text-base/
                • Beam_NetVars.lua.svn-base
                • wiregates.lua.svn-base
                • WireMenus.lua.svn-base
                • WiremodAdmin.lua.svn-base
              • tmp/
                • prop-base
                • props
                • text-base
            • Beam_NetVars.lua
            • client/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_modelplug.lua.svn-base
                  • cl_wirelib.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_modelplug.lua
              • cl_wirelib.lua
            • server/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • modelplug.lua.svn-base
                  • radiolib.lua.svn-base
                  • wirelib.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • modelplug.lua
              • radiolib.lua
              • wirelib.lua
            • wiregates.lua
            • WireMenus.lua
            • WiremodAdmin.lua
          • effects/
            • .svn/
              • entries
              • format
              • prop-base
              • props
              • text-base
              • tmp/
                • prop-base
                • props
                • text-base
            • jump_in/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • jump_out/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • thruster_ring/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • thruster_ring_grow/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • thruster_ring_grow1/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • thruster_ring_grow2/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • thruster_ring_grow3/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • thruster_ring_shrink/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
            • thruster_sperm/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • init.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • init.lua
          • entities/
            • .svn/
              • entries
              • format
              • prop-base
              • props
              • text-base
              • tmp/
                • prop-base
                • props
                • text-base
            • base_wire_entity/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
                  • shared.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_iballoon/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
                  • shared.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_wire_addressbus/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
                  • shared.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_wire_adv_input/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
                  • shared.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_wire_adv_pod/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
                  • shared.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_wire_button/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
                  • shared.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_wire_colorer/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
                  • shared.lua.svn-base
                • tmp/
                  • prop-base
                  • props
                  • text-base
              • cl_init.lua
              • init.lua
              • shared.lua
            • gmod_wire_consolescreen/
              • .svn/
                • entries
                • format
                • prop-base
                • props
                • text-base/
                  • cl_init.lua.svn-base
                  • init.lua.svn-base
          • entit

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