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.
colbypopkie, vmskustom, Donald Drumpf, rex_niro, BigWAT, demirer123, MLGpro80, thekeyman356, thekeyman356, asa_randolph, 2448141214
Submitted by garrysmod.org