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.
SnoxhGames, Aske, amina koyim, 私は同性愛者です, (ARKHANRP) | MohaXx, shradha.keshri, major daniel, Ace, E2 Ghibli, MAGIC→BlacerTv←, ペクスイー シュ『Pekusuii | Shu』, matix, Redvare, Kaname, TVP1 - Mirron, [TW] gunman435, Hajt, Alieni, [LBRP]Altheron™, Rąlҽx91, 遗失的钥 -LOST KEY-, nullified, Marius (HamsterOh), Herr Sturmann ✠, Tomekb530, < blank >, lucaro2708, Kirby, Jan Tuck, Denz, Erick, Sergey_26rus, deef, KaiL, aa, ⋣Óheppni⋢ Xdeposh, [LulzP]Denz, Captain Patrick, Ziddy, Momox, Richard, gun, TheMerkyShadow, DieEnte, Segecos, LegendofRobbo, PB|Dedruss, PichotM (Matt), My Dime Is Up, Zombie +1 others