This download looks like a lua file. You need to place it in your lua folder inside the Garry's Mod folder.
You should end up with a directory structure similar to below:
Don't know where the Garry's Mod folder is or how to extract zip files? See more useful installation tips.
kotel Emi (cat Emi), acquy555555, petukhovdmithry2018, eliseev-valyusha, desinteresado124, TitanMnsM, screwball, Ultrastar 1, Ultrastar 1, davechanderpaul, davechanderpaul, ProjectDiesel, [Ne'A] Sir Xoranes, ChiefBeef14, Pr0 ZombieKills, TAMT145, Willows Landrunner, Lia, lil' tip, NSA Surveillance Drone #3, KellanKelloggs, ( ͡° ͜ʖ ͡°), Swissknife, Scratch, odiemitchell, jagripisti, (S.o.C)ShadowK3, Wolfman19682005, Darkwolf, RGM, Lolcats