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.
wailik2003, ♕Vegeta♕, Pingu, MasterOfCraft, mastah7991 #TEST, [FaZe] Crimsonal, mrstashe, Jéjé le tech, olisempl, diamondmaster055, zeno900Pro, zeno900Pro, Robdk19, playmill87, sogungaming, cami_batistuta