overpowered_turrets.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
          • overpowered turrets <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• overpowered turrets/
  • data/
    • advduplicator/
      • flame turret update.txt
      • flame turret.txt
      • power turrent v2.txt
      • power turret v2 update.txt
      • power turret v3.txt
      • power turret_artilary_v4.txt

mangoman