This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons 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.
garrysscp, mjolnirlucario, ST/POLATALEMDAR!, sugu341, metalblackalone666, 暇潰神, gyobo2019, sdavid.sf, ★De1zzz★, ajo.mj3, KRZ | csgocases.com Luckycase.pl, ultima_sword, antoneusz8 key-drop.pl, teufelin06, rexirex1212, jeremie, jdsc123456, soviet_artyon, alekseybeker2018, scdskol, coreypeace935, sergiomagana2013, Harambe Uchiha, *DnG. | V I O L E N T O * ^ !, J.L MASTER, drake9306, inkling gui, Regulate, nicolasthegoanimator, 03kj20f03232, markovasiljevicmdtm12, Galacktik, joaopirocamole27, Soslu Pizza csgolive.com, brunoalbuquerque698, TheMisterBeard, RandomGamer10000, RandomGamer10000, leo08the22lion, TROP_SALé, yousef.akbarzadeh98, ml956339, CockTM, Jetfuel can't melt steelbeams, harrisonrmoss, red1990joshe, anonymous, HoDrain, yantomaskovic.abcdegf123465987, Dominik12321 +844 others
