Garry’s Mod is a sandbox mod for the Source Engine. Unlike normal games there aren't any predefined aims or goals. Players are given tools and are left to entertain themselves. The player is in a world where objects can be created and destroyed on demand. Where people can be created and destroyed with the click of a mouse. A world made for him. A world he made.
its a patch for garry's mod 9 for other people who have trouble have it on steam just go to steam/steamapps/sourcemods and you should see gmod9 folder put gameinfo.txt in it