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.
dsx3000, joker128, [Earth Fleet] The Doctor, C-dink, eliseev-valyusha, eliseev-valyusha, ivan_power88, andreyroolet, snakevenom95, xyukio, Suprem Cmder Rê, ZAMOSC102, Heckelex, Yoyot64, Doctorplay, [TTF] Amn. LeePalm1943, тѕсм.[SG-1] Teal'c, тѕсм.[SG-1] Teal'c