When you begin playing (after a length of time), you'll start with 5 lives shown in the heart-meter at the top of the screen. If you fail to pass a level you'll lose a life and you'll be given the chance to buy extra moves or try the level again. Each time you fail, you lose a life until you completely run out of lives and your heart-meter is empty.
If you want to continue playing you can buy extra lives, or you can wait 30 minutes for a life to be added back to the heart-meter.
A great way to get some extra lives without using any precious Gold Bars is to ask for help from your fellow Candy Crush Saga playing friends.
If you have linked your game to a King profile, you'll be able to connect to a family of fellow King players, who are all keen players of our games. Ask them for lives, or send them some as a goodwill gift. Pass it forward and you'll see some generous magic happen with your fellow players. If you don't have a King account, you can link to your Facebook profile. Share gifted lives with your friends and family who play and also have linked their game to their Facebook profile.
Tip: When you send lives, you don't lose any of your own, but you can only send lives if you have at least one life.