Play the game "Halo 3" online by signing into an Xbox Live account with a Gold membership, launching the game, and choosing one of the multiplayer options from the game mode selection screen. After choosing a mode and defining your preferences, you must wait in a lobby until other players join the match.
To play any Xbox 360 game online you must have an Xbox Live Gold account, either through a recurring subscription or by purchasing a membership card with a preset enrollment duration. Playing "Halo 3" online requires a physical or digital copy of the game as well.
Begin by signing into the Xbox Live account with the Gold membership and testing your Internet connection through the console's system settings. Launch "Halo 3" and choose the multiplayer mode from the list of options in the main loading screen. It is not possible to play the campaign mode online with other players, as it focuses on a single-player experience throughout many of the missions.
Each multiplayer mode includes different rules and requirements, such as competing in a team or against all players in a death match. Each mode also requires a minimum number of players to begin, as they all center around competition in a unique instance rather than taking place in a persistent world. You may invite other players from your Friends list to join in the match, wait for other players to join a match you are hosting, or join another open match.