You can play the Scratch Cards by tapping the Scratch Card icon in the lower icon tray along the bottom of the Bingo Pop home screen.
 
Swipe your finger or click and drag your mouse cursor over the ‘Scratch Me!’ area to reveal numbers. If the revealed numbers are on your bingo card they will automatically daub for you. You can win a Bingo, Double Bingo, Triple Bingo, or Mega Bingo on a Scratch Card. To view the payouts please tap the ‘?’ icon in the Scratch Cards screen. 
 
When you play Scratch Cards may also earn special puzzle pieces just for the Scratch Card puzzle. If you get all the pieces for your puzzle you can +1 cherry for your Daily Bonus
 
For more on the Daily Bonus please see How Do I get More Cherries?