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.
animerychlicki0, Barsuk73, belfim10, Nightmare Godzilla, Law, SuGa, Ace of Kings, Doritoborn, justgamer, batosaisangpecincang, Slyg00se, *M.O.T.A* WolfBlood L'irlandais, BlupBlup CSGOEgg.com, NeurofunkPunk, Jeffrey, Snog Dog, Sora Tatsuo, Razorroboham, -[WEED]- iTz420TimeE, Mewen, ★Silver Lake★, 감귤 작작먹어, sinka1031, sinka1031