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.
Alexandre, Persona, benwolfe7783, ercan2, Santhosh, ms.mentison, Artūras, Apsy13 | Gamdom.com, xXTurner | LowOnAir™, SlingingNeo, Rixo31, xsdaaaa23, goodstandart, Hardwell, [URP] Jonas Drain, shakeebprince, sayedziad, [L²:RP] Flashplayer, MasterLord140, didier.a.pulgarin, alexavil, Orlög, PonyEB, -Speedy, Takahashi