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.
Prodddy, Mister Arthik, emir tezer, Mr. DusMees, filip sergant 420, samways.ben, ♠morzh.petya♣, arthurdaniel911, GrackGreanZ, [email protected], markvarro86, 悲伤的爱, Bravo2YTpl, [GD] Haru59, yunaldo32, Sir Pickle Phillips, artak.sargsyan95, Dester, karloka ✅, DeadShot[DS], [GISNAC] Killer Rosa, LAHunter99, CT Domi85, angelo, Redogg, SpongySpiral