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.
۩۞۩kyleweasel۩۞۩, Gulyabani67, misty.atwood31, Den, keonjj93, dogukan_aksoy222, LB MCDonalds, noumi448, homitomigt15, akram_aissa, сМаКуС & 35, Abraxis Virus, Warhammer, MetalKing, Spg034 hyplex.co, iconebg, wachis.17, a1_ahmed20, kirpszas899, vasgolen, The Orange Dragon, loupgarou_e666, Desert Eagle, ytp123, riza4, ziuzinas