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.
Letmego, tippytoe018, lNitriix, [URP] Jonas Drain, Jeremy Clarkson CSGOirl.com, kabaserkan14, Giygas, Rexani, [Ere376], Ze Penguin Doktor, MasterShake, Jay, WOOOOSHH, Tobe, Endorsed Network, Sabre, battlefield 4 russian, ⑨Shendow, [=EGC=] Lukas, MrKuBu, Andre, xbeastguyx, [CE] Baus Kingski