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.
eddielemus76, rasystem2030, melihcakar666, mateionk, rlz, fetty fapp, Gravity Cat, =[RG]= Sidorovich , Wedtunk1, Minx, Dnjido, native aboriginal, Snake In The Grass, mochi, Bad Hombre DC, LegendofRobbo, CONRECON, Perfect バービー