You have 5 lives. Your lives counter is located in the upper left corner of the home screen and shows you how many lives are left.
If you have no lives left, you won’t be able to enter a level. You regain a new life every 30 minutes. If you earned any lives from various rewards, they would be located in the Lives Bank in the bottom left corner of the home screen.
You can get Unlimited Lives as a reward that gives you unlimited use of lives for a period of time.