This download looks like a lua file. You need to place it in your lua 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.
TR1F1N1TY, SUPER TOST, [NG]★Panther★, TheManTheMyth, [FG] , F2P N00B, TAILS988, Tubbz, [T.A.B] Springtrap, ▲ TehFunkyPotato ▲, Nraaax, Herr Spaztrout, [KGN]KyrusGaming, D.ツ, mubasher.shaheen, Dr.IrishDan, Darth Vader, ☃❆[SM]RazorNight❆☃, SFAriel, Woky, Mongrel, Clockwork, Neon Umbreon, BOB DYLAN, Zuruuaku, DieAnotherDay aka Mr. Coala aka, James™, Rodinavian, Stealthy Zoroark™, PonyEB, Matt-Senpai, Manni das Mammut, Joy Ferret, Solar, Yoh Sambre g-box.fr <3, Nidolai, Nidolai, , Mr. Moostache, [LT-RP]BestOf, Mr. Brightside, Kolorek