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.
w.d.gastertejode, xoraz, Kníža™, Kníža™, new.horse.world, gabybarrocos, denis.zdanovich2006, yan.tretyak, domd31675, _temza_, nickcorello, ariasmichael22, banettetejode.yt.2.0, banettetejode.yt.2.0, tomascano.romani, RebReg, gavintron99, graslukasz, sasha.kochergin.04, wuki.vucko, denisalexandru00, M A C, Mafiozer_3000, arianasheghi2377, reephn, Mr Serbian, minerlorenzo, MCGamer2006, alejomolina, alejomolina, Lucas Camarotti, TKCOWO, herobrinevlog, d.lukasz05, Suzulaugh, +*Cute_Boy+*, timikunik2005, kriszimiszi122, romantyczka64, denisalexandru00, lmpzy, alexshulski, mjcvandyk, Blesk, demon spy, fenix2, cute.boyammar, silvasandro26061972, nica.alex.35, GENTLEMEN SPY[ASİL TR] +134 others
