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.
๖ۣۜLegride, ★Hi I'm a pootisbird★, boi, 가면라이더, [(Matoti51)], Bad Bunny, Northy!, Jason, Linkl, SWED_CODER, Lostinpugs Ellie (P.U.G), dufa, Rerabox, syno04, Dragon58Whisper, .vurk, WillH, MAGIK, ★ M Arisato ★, Jagged, ★〖C〗〖R〗〖4〗★, Jeff, OP_rah, DrankMySip, uck foff, Fear_Dragon I hyplex.co, Barthez GoldGoal, Kevlar, BlowScales, jojoreen, BlueHairedNinja, WolfG, Lord Splash, sans, [LG] Rews, [LG] Rews, Ccsdkb, Salad <3, , Dogsailor, Killeo64, Killeo64, bbenjamin1702, M A L W A R Σ ツ, So Doubtful, So Doubtful, Slighterer, Slighterer, TOO-BEE!!, TOO-BEE!! +189 others