In Watch TV mode, if you have a Cable or Satellite box, most of the buttons will actually be controlling that device.
If the sound comes through the TV's own speakers, then the Volume and Mute controls will affect them. If you have a separate audio system, these controls will affect the sound from it.
Touching the exit button will take you back to the main screen, where you can change language or create a new profile.
To switch to another mode such as Watch DVD, touch the appropriate symbol on the mode bar.