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
-
flcl <-- Addon folder!
-
e.g.
-
lua
-
maps
-
materials
-
models
-
etc
- flcl/
- Info.txt
- materials/
- models/
- flcl/
- Canti/
- Canti_arms.vmt
- Canti_arms.vtf
- Canti_arms_red.vmt
- Canti_arms_red.vtf
- Canti_head(blasted).vmt
- Canti_head(blasted).vtf
- Canti_head(blasted)_red.vmt
- Canti_head(blasted)_red.vtf
- Canti_head.vmt
- Canti_head.vtf
- Canti_head_red.vmt
- Canti_head_red.vtf
- Canti_kinescope.vmt
- Canti_kinescope.vtf
- Canti_kinescope_red.vmt
- Canti_kinescope_red.vtf
- Canti_legs.vmt
- Canti_legs.vtf
- Canti_legs_red.vmt
- Canti_legs_red.vtf
- Canti_screen.vmt
- Canti_screen.vtf
- Canti_screen_bsod.vmt
- Canti_screen_bsod.vtf
- Canti_screen_cam.vmt
- Canti_screen_sign.vmt
- Canti_screen_sign.vtf
- Canti_torso.vmt
- Canti_torso.vtf
- Canti_torso_red.vmt
- Canti_torso_red.vtf
- Canti_wings.vmt
- Canti_wings.vtf
- models/
- Canti.dx80.vtx
- Canti.dx90.vtx
- canti.mdl
- Canti.phy
- Canti.sw.vtx
- canti.vvd
- Canti_02.dx80.vtx
- Canti_02.dx90.vtx
- canti_02.mdl
- Canti_02.phy
- Canti_02.sw.vtx
- canti_02.vvd
- Canti_03.dx80.vtx
- Canti_03.dx90.vtx
- canti_03.mdl
- Canti_03.phy
- Canti_03.sw.vtx
- canti_03.vvd
- settings/
Shararamosh, yung trashi, sampleemeril89, FiveEyes, mrlanky, Willbur, Taokakabom, Canti, Eddamantium, Lowd70™, Kogara, Blue Burrower, Greenbox6, SK, Solara ^_^, phasma, phasma, uzucake, samwisekun, permanent name for inconvenience, nemu, ChickenHawkSama, pooquats, Swagu, Space Dandy, Dendei, Idiot Box, Lava, Tom The Cat, Fhufuu, Xeality, Dorothy Haze, pete0509, Sabrejack, basicguitar, MiahB, Hokie, MGZEVANGELION, 바나나226, Silante, atomsk100, Neko Oni Nya, Robo, Robo, lady arizona, Un.su.re, lois_soremata, Dei Vocationem, PC Viking [2], ImAfraidOfDoors +41 others
