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.
timmy999timmy, HanzoMain, stefanPRO, Doom_My_Hamburgerz™, Taru, My name is Puzzle, BoiledPotato5426, sweeenii, TermyBird, Hodux
