This download looks like a save. You need to place it in your saves 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.
nnn0611, XenoNuke, 277141, MrPlayMaster, lidok.ppp, 277141, vladimir04ingilizov, kirillov-2006, radik_melnikov, filipka.ivanov.2016, macekzn, lf1498, www.andreybarkov, TheIronGaming, ☠FoxyGaming☣, ibnucandra395, pro125gamerbg, exempale, Vtgordon, pro gamer PL ͡° ͜ʖ ͡°), karub.burak, sitkinator, sitkinator, sitkinator, sitkinator