Each power player offers a special ability to help you achieve high scores.  At the start of your game session, you will be asked to choose a power player.  Burst as many bubbles as you can with the chosen power player, and when the power player meter (on the upper right corner) is full, tap to activate!
SB is your default Power Player.  Patrick, Sandy, Plankton and Squidward can be unlocked with Krabby Patties.