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.
Q0GAL-7QJLH-DI08I, brynparker2017, nietonahuel211, , [HeenokFam] NawA, Gryphon 1-1, •Fellix•, [SNS] Xwatch1009, LIL TEETH, Acecool, ChrisChiller, TheRudyFox, lukinhb, lukinhb, lukinhb, Edmond, Ryu, asdasd, Free2Play