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.
..:[G]Luk:.., Sart, Sart, Lisichka, [D2TM] LegalEagle, Бухачу!, petrochered, where_is_your_god_now, benonroblox, Mr.Siemiite, zfadarkness, sandiegoklassik, BobBro, Crazy-Wolf, Drogo93, DrSTaTTiK, tank21696