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.
leonberna, Macthelost, BlackHawkTP, lord of empire, lord of empire, کǺпd€Я, BDR(BlackDenRus), turkufiliz, Dr. Savage, NightAngel, sүяɛҳ ℛℴsℯ™, Shalashaska, aalik1066, Ｓｖｅｎｓｉｓ - serverhell.cf, SpyKillerYT, mcLAREN®, mcLAREN®, Respite, Icewine Rose, Mike The Comrade, Reverend Jesse V92, Reverend Jesse V92, damir.balgazin574, bm killler10 ☠, borisbritwa91