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.
wakka, ben, AF_SFT, paphatchon.01, escaperx, ambitiousdeath, tayebehhadigol1, mohym806, el_insano_mas_insano, AntonyBel, ScreamBlood, Gio_18, blancangodoy, khueljaji, kirikokamori8, errorbooysen, yasin.mmmm.0371, Demi_cool123, edfrhuyt, bethyleo, leoncheater, hsx125rr, Not bob, z02, Dvaughn2261, Snqk, tvreal_2010, 2073213793, nolanwrussell12, trxshnu, rasystem2020, Alacai, Сергій Горобець, HolyHeartBreaker, Max-Floppa, Brick, Wylx_The_Bobcat, XXXX, 2002, 液态原子屑, kluska, ElGeometry, ivanvel2011, hmo enfegarat, Quasar, Corporal, [1993]Duangeor, [1993]Duangeor, АнАкОнДа_YAre, MyTigerLily +22 others
