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.
Reza8772, emir tezer, ☪ şehmuz cicikuş ☭, shiamirre, Sevv, Hotcher, Neptune, Sir Deez, Sir Deez, tariqsw69, elcanallon.92, breinertoro, ryanpeterson933, General Who, General Who, aglaro, The_WonDeRing_Boy, Ghost Rider, miniditt, DJ Prodigy & Vinyl Scratch <3