This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons 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.
sansไทย, Prisky, =pb SpookyWagen, QTG坑, paolobrianmendoza, xXxSwAgLoRdXxX, killersonic582, ramy.senane, jm.rodriguez03.fernandez, De Butcher, madalinstanciu03, SkipFighter, edenarmar917, veroi, Pvt. Dorkus, truepopperman, DarkShadow126, SpoopyLegs, andreistan2077, Hds46, eshemura, O'Nesix, ikosmid