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.
Mr.ProousMan(ITA), darkstar12374 | dogry.pl, ^1Remove ^0Kebab, Boost, antoneaggabi, alannowak112, ░▒▓HoverCat 0768▓▒░, Raymond Tracer, xetatorr12, Rush Bee, TheDoctor, Sgt. Interrobang, madman862, wipster hybrid martin shkreli, フラックス