The Exit button is only available on Android and is not available on iOS. It allows you to completely close the application and prevent it from continuing to run in the background and using device resources.
To close the application, open the Menu and tap Exit. A confirmation message asking "Do you want to exit Sygic Truck & Caravan Navigation?" will appear. Tap Exit to confirm and close the application.
Alternative method
On both Android and iOS, the application can be closed from the recent apps screen by swiping it away from the list of active applications.