The sleep timer is perfect if you want to fall asleep while listening to a book and have it turn off automatically after a certain amount of time.
The sleep timer is represented by an icon of a moon with a ring around it. You can find the function on the right side of the player. Press the button and choose how long you want to listen to a book before it turns off.
Your book will turn off automatically when the timer under the moon symbol has run out. If there is no timer running under the symbol, the sleep timer is not activated so make sure to check for that.
The next time you start the app, you will be greeted by a helpful function that makes it easier for you to navigate back to where you fell asleep.