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.
I K A Z E, vonell12, lelalelalela976, w0nderful, aldaveronika35, esnokusinfiltros, elnehuprietorimoli, nati1020, megustanlaspapitasxd, kjuaki, deckssiv2, odofkgididoid, marcelo.espert, caleb.jackson0108, ana25092001, nottbnrblue, josemigue3643, rosumarioara210, ghostdzpro9, JOZU38, laguafrancisdominic, Justchill, Fridix, Kitsune no Okami, Guy, aromFM, julien, arab, rachelcgriffin21, Аномоно бо, guculakdenis, Tizianojaja_YT, robotech82, hank j wimbolton, blackroblox83, zeus1975, turbox686, KaczeqBajceps, axelelnubxd, tortugabluepena, EliApplen, benpibeniamino, leandro.sm82, MalvinasArgentinasNashe, Snowy, milkandcookiez1515, jeffsilas420, gabrielkrauss98, javi_cou, guilherme.oliver +3214 others