A flag is a certain type of game object in ROBLOX. Flags are mostly used in Capture The Flag game, but some people can design a different type of game that has to do with a flag. To capture a flag touch the opponent's flag. This will give you the flag as a gear object. To capture it you must go back to your flag and touch your flag with their flag. This will give you and your team a capture.
Generally, you would have to carry the flag in your hands back to the base, preventing you from using tools. Exceptions include Underground War, where you can carry the flag on your back, letting you use your tools.
Flags can most easily be added to a game in ROBLOX by selecting them under game stuff in the ROBLOX Toolbox. Flags come in default colors such as Dark green, Bright blue, Bright yellow, and Bright red. They can be changed to custom colors though.