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.
`K1, sviat125, Макс, (youtube&twich)TheBlackPrice, SAS41, rere.lana8, rere.lana8, Oxxxy, GOLDEN RAZER, vladilko1204, kaktus33221111, maximok, max.david789, rostik.pivovar2004, Lesm, bariga256, rage_unturned_14, 99orion99, Gokui 瑠璃, Vitos21