This download looks like a lua file. You need to place it in your lua folder inside the Garry's Mod 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.
kgergo5800, Wippy, ridha23dida, -:=БАТЬКА=:-, Drew SlxyZ, TheIronGaming FNAF Endoskeleton, HesNotorious, Flash -, Loading Idea..., I Я ДШЁSФMЭ, Alarm, lukinhb, lukinhb, lukinhb, Johnny Whinkel, Jurisdiction, kirbygame126, Mr.Gravey, Ar.Lam o_O, ҉;GBSFM ҉;, wheresmygui, Puggilicious, Sokkah Abdelkader, Sokkah Abdelkader