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.
2dank4u, thangsatthuvn, mariusz.lisik1, maskered_2005, nerueditions, danielrx28, lisik-mariusz, zee.ekspert, gucio9, pp08250, MaxPro2100, Maple, crepeerxd, НикитаЖдановКТУЧ, SniperGANG, 1293906533, lowteen2548, peak_rock, nadermamdoh55, GingerGaming, 1648111684, mustafa.omanovic2000, mister Wong Jr., mister Wong Jr., sadfto3, evanadi20, MPPL2005, MPPL2005, 80tanergunduz, mineoski14, nizamazrol7, akiramakasuren, nutaui12345, =.=, Dr.Beat Der Bambuschwinger, deez4390, therayninja, ziadsayed07, kentam655, chaodeknoi, joepooh69, youssefahmed1591, youssefahmed1591, sebasg12321, xXEfrain10Xx, Marko_, [Anti-VDT] DJtoburlao♨, [YS] Bartman | NOOT NOOT, lilpaladin1, XBC4000™ +2 others
