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.
vgc, Figi_Gold, olepirhiki2008-2018, kandigim, Jake, Justin, Justin, srteam00101, kakagameloft3, Tvoi timmeyt, Ozziz, joker666.1337, Zaheer, mattpeckron, Beyondyung, DJ PUNK, zzz2312412, gustavoacunalira1, sirgeivich4, James85, saba.beroshvili, chvassumpcao, Darkpuppey, HIKINITE, pacanok228, stevie jones, Honvai, Karo Diamond, xXMLG-PU$$Y-SL4YERXx, ninjapig26, solitaire45, KERRY