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.
nicitaoficial, =CCG= PBeezie80, nightrainmusic, Gaulex, TazManiia, QTG坑, tepikin.egor2016, Dr. Blueling, Defner, EKIDINA, Ø Mr4Prox Ø™, yanis.rozand, RudyX, HibikiKyoya, letop06, Alarm, TripleGun, [FR] Tiboxxi, lukinhb, SeeTwo, yasser, insanekiller1, kipper, [kkk] Dick Dickenson, Sokkah Abdelkader, Sokkah Abdelkader