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:
Don't know where the Garry's Mod folder is or how to extract zip files? See more useful installation tips.
Сука Блять, PARKER, Hanspeter_, minediamond000, Afrodight, a66208841, shompolovdenis, RadioactiveShrew, Cipher, RileyGame.ru(xprints), Alucard, oRavenix, Pantherlily, Korneliusz, [1.SKM] Platinfuchs, SsjGodBeastPlaysVideoGames, Chest, JAMBOR, Nanook, 상큼한병신, deoxzygames, Erika, rapps, <HS>F.B.I. M!K!, Jd