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.
你爸临死前, nicolahuda1, arianasheghi2377, Rubix339, Tarnish, sssss_23, kacper_betler, mert_killer, silentgangsta04, samboja687, Scout, Tecon, dani_dani2719, re15revisited, ХУЕГЛАЗКА, misaelbravo19, fernando.hpf, Busterbboy, amer.kovac, riybokon, E7ajamy (home, free to play), pussydestroyer, superkaka (HKC), eray_02, LOPREM, Ethan, Freddy, Ghost, Nostar, Sniper, SILENTGAMER, M3SA, The killer of dark [TH], Japalton123, SFM