You have a total of 5 lives. The lives counter, which can be found  in the upper left corner of the home screen, keeps track of your remaining lives.

Once you exhaust all your lives, you won't be able to access any levels. However, every 30 minutes, you regain one new life. Any lives earned from diverse rewards will be stored in the Lives Bank, found in the bottom left corner of the home screen.

Furthermore, there is a special reward called "Unlimited Lives" that grants you unrestricted access to lives for a specific duration of time.