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.
zcb310, [CGC] supercell12, Ed-209, Yimek56, Pokerar, Noorman, greentrigger5436, Artery_Wolf_0505, Dardex, Maul, ThrowingNate, ☆Flavman☆, KERTEMEYENKELE, Lycanroc (Midnight), matyas.koutnak, RTO, ZFPotatoMan, ModiFkrs | CSGOPoints.com, fandegames (Zongo), Koro~Demi, Disturbedskizoi, Seymour, C0mrade, TaigAy, Shadowlink2018, SonicTeam2006, Ordo Skirata (N-11), ChaoticScourge, TNL, TNL, Photon360, khalifamaamri16, KinderEye1000, Petgamer132, szabolcska2007, Supersquirtle6, uber.kawii, (MVG) KMan, Lollics, CheekiBreeki, Sergeant Rotor, Papa Fudge, Legend, ThreeEyedFish, Charon, Keemstars Hypocricy, SpaceAlpaca11, ohstarfinoh, Mork, Lewd Lawliet +118 others