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.
[BG:O]FreddyPlaysYT, TnxBT, AlexManiac, Raxshi, James, [PG|Owner]Pckool, Owzmo, Leon, JavaNava2, Mr Panda, FiveSeven, ToXiiC, martin.drelich1999, FuRyX, KX | Taiwan Jeff, KX | Taiwan Jeff, KX | Taiwan Jeff, KX | Taiwan Jeff, [FR] || Boris ||, Бен Ладен*BenQ*-CAPITAN, -NeGaT1Ve-, |-ICE-|Shy Guy, [IM] Nobody., Łeød™ hEh CS-GO.BG, kk, BoneZ, ☆ HazardSkii ☆ ( ͡° ͜ʖ ͡°), [RDF]Aekola, Lumii