Template:Simple Application Activity Lifecycle
One of the application component type is called Activity and provides a screen for the user to interact with.
The activity object could be created from a subclass of the Activity class or one of its subclasses.
Based of the user input on the activity screen, the operating system calls into your class some important methods. The figure from this source illustrates the life cycle of an android activity component.
Here is a sample that illustrates the activity life cycle.
Managing the lifecycle of an activity is defined in the how to build a simple Android app tutorial.
Furthermore learn how to achieve internationalization by understanding this code. Try to modify it by adding a new language (yours, if it is different from sample's).