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.
Charge, monochromix9, Bonqueque Demarcus The III, matheuslopessamaniego, UserUNP, Pacpernik.**********************, take باعبوصة, StefanRue, ZLATORZ, SperWal, Neslo, cream, Plazmunky, PikuBerserkerXZ, Shadezz[CZ] d-.-b, niketheshoes, Tommy Tom, superpuro, the jigga man, touhou, That Box, necromancer, FRANK金OR, The Zen-Aku, Brent, Saman.exe, BiBiModz, [MRTB] DieselGaming, Datsun 240z, ihaveawindows, attila.karsay, Smoochie, NovaTenSoon, christopher.valdez008, GalaxyyOne.GSX, Dekapote, Mr.OldschoolGamer5000, EnSarDrGn, grewok, hakunak12, vaultier0, Menzel, IntoTheWild1995, Fbgamer3837, IntoTheWeed1312, yasin.nla, skoupidiarees, zinanchua, mmuktiali0, mmuktiali0 +2645 others