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.
aayushmanvijay8, serzandevrim, DG9, kernel330, John ballzinki, mleko99772, carapochaortencio, kupcik15, 一只蔡徐坤呀, 솹파피, GIJOE_tanker, neljh, daveysterkman, советский, choto, caminugamer, vova2003165789, Deivis Salaverria, Deivis Salaverria, niraamaymd, longshanks_mcgee, FOXIGG, RedShadow3060 gamehag.com, nicecrafter0507, bernaljohnny3, Dominic W, BLINDÃO, [MFT] Xtazii63, Russiaman, Bariore, mr.sandbox, RamzeS, RamzeS, RamzeS, edgefighter2017, Yordanovvv, Marco22, antoniusevans93, Conar, rannnks, DIDIX, Grey Silhouette, ElPatriota513, Resertos.de | TheUnknowns || Leo, Micr0iX, Bezimienny_33, kubikmachac, Remix187, noodlemop, noodlemop +56 others
