The System Menu (O) will open a User Interface window with Quit, Logout, Characters, Options, and Cancel. <Quit> will close the game completely, and has a 10 second countdown, during which you can cancel. <Logout> will take you to the login screen. <Characters> has a 10 second countdown, will log out the current character and take you to the character select screen. Other characters can log in immediately, but there is a delay on relogging the same character back into the game. <Options> opens up the Options Window, and <Cancel> will cancel any action.