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.
squidy.8, __Sylwek__#oWn, Source SDK TV, Galacta-X, Pomelo-Dilina, naxoshome, nurlybek, kemleyo-salemsiz, kemleyo-salemsiz, =[o.W.n]=Castor76TheSoldier, ❖ MAX ❖ I ❤Toriel, Jecop Lonsan, [SXB]_Alesha, Sonicteam998, Sonicteam998, Sonicteam998, MainKo, Arki Red , [email protected], LazerSpy