Coming close but you still can't beat that level after numerous attempts? Or maybe you want to keep playing but you have no more lives. Coins can be used to purchase additional moves in a level or extra lives to continue playing if you don't want to wait for them to recharge.
Coins can also be used to purchase additional Power Ups to give you a boost in a level.
Coins are purchased with real money, but you don't have to use any Coins in order to progress through the game.