This download looks like a save. You need to place it in your saves 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.
ⒽⒶⓁⒺⓃ Aяcнangel_510, [24th] GammaGamming, ilm9001, §『㎖i_CRo ζoFt』§ | busy, Mudchop, Koray // Fire, SimplyPXL, ☣[DFS]jcash☣, Monkey Lover, Karll, iFireMaster, lonely19682005, ❮/RedTailedHawk❯, a proper madman innit, CMDR Renco, kyle.stokes321, As a kid I looked like a carrot, Teh Hatein, Ickyman, 감귤 작작먹어, Ж_Ж_ЯłÐÐłϾК_Ж_Ж, Фрэнк