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.
[FNG] MrNockz✔, Ravelord, *OCB* Pekusuii | Shu, [FNG] cigarettes, [LƑƓ]mew™, Taco's from the Sky, finnabehelladone, Ceeks, Limpmulerider, [GL] Zeeptin, [GG]Sonic Cloud, katooosha, { TTM }, Ivitokun
