dead_ringer.zip

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
          • Dead Ringer <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• Dead Ringer/
  • info.txt
  • lua/
    • effects/
      • uncloack/
        • init.lua
    • entities/
      • deadringer/
        • shared.lua
    • weapons/
      • weapon_dead_ringer/
        • shared.lua
• readme.txt

# Cyber / EKMEK ARASI TOST /, Contrafell, ITS A MEME, isaacsican913, Player-0, BlackGhostTR, xXxSkeletonTWxXx, Vademon09, PlayGames Doctor, [TN] Radio•Active, Mlv dominik, sans81774, TCM, Void, feierblas, soggy french frie, KyrieTheWolf, KyrieTheWolf, KyrieTheWolf, Sugaros, Mine nerdz, Marcanda, Buff Rick!, Ukas25, Animeat, ^4jakey0804, PotatEgg, marshall, I Bims Schnappi, Alkamis, Sylauge, Rick, Bass, Ariana Marie, Patrick Smith, CrØwπless ♕ ツ, Crxfan, Brandi Love, bonnie br, ✪ JockelHDツ, Echuirwen, Araclutch #GetFrekt, Execute, Flips, Schlitzer_Mc_Geurg, CryZz, $leWelzelle$, jorgearturo10dc, |LTD|Dizzle®, KevGamer +105 others