The virtual joystick in the lower left moves your character. Tap the Switch button above that to change attacks, and hold the Switch button to change characters. In the lower right is your Attack button. You can attack on both sides of you by tapping the left or right side of this button. Above that is the Dash button, which lets you fly really fast. Keep in mind, though, at the beginning of the game, you've forgotten how to use your powers, so you'll need to unlock all of these abilities before each button becomes active.
In the upper left are your Health and Power bars. If you run out of health, you'll start over at your last save, and you can only save your game in special Save Rooms. Most of your superpowers use up your Power bar, but you can grab pick-ups to replenish it.