Once you visit the "Diablo 3", you will be able to see the character selection page open the list of games. Players can get someD3 guides in diabloiiigold.com
Click the "open game" button will allow you to choose which task performed. Please note that regardless of the progress of the other players, you can only choose to join a task that you have started.
After you click on "Join Game" button, you will quickly progress and the same task with other players within similar level matching. In co-op game, you can communicate with up to three other players with the game (of four players to members)