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:

• steamapps
  • common
    • garrysmod
      • garrysmod
        • addons
          • data <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• data/
  • adv_duplicator/
    • sumotori_basic_2.txt
    • sumotori_bot_8.txt
• Info.txt
• gm_buttes0084.jpg

[सुन] Jashfuk, Dr_Cynical, tokosmark, Kydesn1k, Jeffrey, [Metro], Sora Tatsuo, Catom, иоcтёdоцт, Spess Mehreens, GalacticHam, Dr. Porffesor. Sad, Alexander Alvarez, Erstarisk, profX