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.
Eden Hazard, wow0warriors, ✪ Brightness, Plant_Craver, leam414, XiloFox, Baconmaker, chlrud951, youtube.com/JripDaGamer, TheGamingCharizard, Arctic0ne
Submitted by garrysmod.org