I pay to restore hearts, but then when I go back to the lesson, it sends me back to the very beginning. Why can't the restore hearts be there all the time, instead of just after I had to do the whole lesson all over again? When I hit the back button, it sends me back to start all over, what am I supposed to do after it equips the new heart?
You need to buy a heart refill before entering into a lesson. When you have one currently "equipped" (it will say Equipped under the icon in the store), the option to use it will appear next to your hearts in the next lesson and will continue appearing until you consume it.