In most games you'll get energy to use for each mission, but in Candy Crush Friends Saga, you can keep on playing as long as you don't fail. You get lives, and you'll regain them over time, and only lose them if you give up on a stage. Which, if you run out moves and don't want to use gold, will happen. It's a pretty good system, as long as you stay focused on your target and make smart decisions, you can keep playing for hours.