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.
Bigsmoke Fat boi, karenkismiran, adolfe12344, anonymoususer2246, СУМРАК CSGOUpgrader.GG, ☭kion badili soviet furry, nisaferhat, tegan, MIKE, ponl1234, maudf007, chahingrissi371, v.frantishoff, morgan27.4, www.hangpony8889, opposingforcegamer22, someone, kyhuong71, shulgamaksa, Intruso, augustovihari, osmanayg, Deko desu, islam23annaba