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.
gryZor4000, djroxrox, swarshilder, Deity 8678, ORANOXE, M1notaurcz, SnakeSVx, Twizorox, [LFG] Ancient, тѕсм.FIREST0ЯM, alejandroavila438, joecox1231, razzan, Col. John Sheppard, cdc, 별이, [AN] HIFFTY13, Mr.RESJ, Noname, Noname, Song, Alarm, §『㎖i_CRo ζoFt』§ | busy, PanzerKill, Rafa.black.70, DeathXRose, juanelolo, juanelolo, Arlisbloxer05, Haazey, IAmDanya, Ruzzy, |-KPH-|, ynK, L3M0N, Comrade_Maks, ﮒ∆ѪѺ۩†, Reverend Jesse V92, Skeleton, ƬǶ∅ℛ∅N∅Ƨ_, Keshwoof, Keshwoof, Keshwoof, Keshwoof, Arki, Arki, kurtis_13_1994, Joe Biden, sinka1031, ⅇⅇⅇⅇⅇⅇⅇⅇⅇⅇⅇⅇⅇⅇⅇⅇ