This download looks like a map. You need to place it in your maps 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.
aszxcde1234, aszxcde1234, Master Chief, ●Fondateur RhoslamRP● SkyRoy11, re15revisited, re15revisited, Mr Soarin, Scrymmery, rongta, Original Shaman, CrazyKiller, killer833426, Russia Greatest Love Machine, keryl22950, Empresario Amway Premium, peaches, milan_luca, ⭐⭐⭐ Sebastian, MrWARIO (dead), alosep-oidualc, etholan.sconiers, Dr.Kwiik, ᠌, Lunatic, Regnum_, Thomas, 2448141214, BRUTTO