This download looks like a map. You need to place it in your maps folder inside the Garry's Mod 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.
hristya.vaksna, Kon4o_XD csgocases_com, hasanemrekocer, create, PonyPlay2004, The Big Trumpet, *-Xienon-*, hensaxd, playboi sharti, Maner, mossesx, tnasetk25, ballesteroaxel173, Xlo0, robidatone, jakub.gminski, pvt Johnston, kevin.cartoon, GoldenAppsYT, Leo, adji.tontondsd, Commander Zuskopo #SaveTF2, The Spirit, Originality, SpeedrunnerMario[LFG], 응너의 의미, ningken, Chloe, Steely Dan, ♥♥ Zoey Clinn ♥♥, Ж_Ж_ЯłÐÐłϾК_Ж_Ж