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.
teryoxin_2000, [è_é] Alvalm, Ausimus, adagiocheese2000, Tourist, leonardbob49, chinjung667, flo, Müz, lollyminegaming, Th3_YahiJhu, ahmed001188, Vl4dy, aivaras.lesvenciunas, jeffthekiller96, Fooltaurus, igonai, antonguru96, KaZzaArack, Ryukre, l.maire c, lonely19682005, Stichyy, [CG]hayche88, Otrillmaine, JasonGamer76, THE REAL FOXY