The picture on the right shows the default BBO HUD screen. At the bottom left is the movement pad. A standard movement pad with all directions. A little bit to the right of the movement pad is the token pickup amount. In BBP tokens spawn in random areas and you can pick them up. You then use tokens to buy power ups in game. The powerups you can use in game are right next to the token amount. Your powerups change depending on what you have bought in the store.
At the bottom right there are 4 buttons. The sword button shown in this picture is the special ability button that changes depending on what character you are using. The red circle is the shoot button, which can be held down to fire automatic guns. The lower button is the melee strike. Finally the highest button in the bottom right section is the jump button.
At the top left you can see your character's face, right under that is the chat button. Next to the character's face is your health bar which decreases as you take damage. to the left even more is the score, with the red teams score on the left, and the blue team score on the right. In the centre of the score is the option button which can also be accessed in the main menu. Finally at the top right is the gun image of the gun you are using, and if you tap it it switches to your second gun.