Lives let you play levels, and they appear as hearts on the level select screen. You begin the game with Five Lives and you lose a life whenever you lose, restart, or quit a level.
  
You can get more Lives in a variety of ways:

  1. Wait. Lives recharge over time. But that's no fun, so how about another way?  
  2. Ask your friends for more Lives. Click “Ask Friends” on the Out of Lives screen, and pick which friends to ask. Each friend can send you 1 Life. 
  3. Buy Lives with Gold. Buying Lives will restore all your Lives immediately!