You start with 5 lives. If you fail a level, you lose a life. If you run out of lives, you either have to wait or buy lives for 12 bubbles. If you want to increase your live regeneration limit by 3, you have to buy them at the App Store. One live is regenerated for 30 minutes each. So, it takes the total of 2 hours and a half to bring back all of your lives from 0 to 5.