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/
basicguitar, MiahB, Hokie, MGZEVANGELION, 바나나226, Silante, atomsk100, Neko Oni Nya, Robo, Robo, lady arizona, Un.su.re, lois_soremata, Dei Vocationem, PC Viking [2], AdjustingPriorities, falseprophet141, gonzaller, diaclone09, pyramidhead395, jabodlj, Manikin Drone, C Y C O T I C, C Y C O T I C, linsops, Croconaw, Croconaw, LMR_1, ✴ Bread, Pheonise, jah_2001, Kamikazi Hero, , Hoodwinkedfool, ZeroKite, Blargman, Blargman, Nopeful, †H△† Be▲Ʀ B△5†aƦD, Chaos Master, missile kid, Zaku II (laggy addon collector), Grampa Walker, Sodapaup, Derpu, Taffy, Nep The Kangaroo, The Rocket Gamer, Courier, Soviet Comrade +2 others
