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.
√[Õriginal™]_Demy99, busermanov5, busermanov5, busermanov5, berecz98aron, asdwdwad, john.wickholm, Doublefurly, yadiel8927, Swiss-bones, nightfury1177, SUPERCACTUS, Dnjido, [HG] How Super Terrible?, [HG] How Super Terrible?, CubicTuxedo, AlexPong