The first thing that is important to understand as a developer is what really happens behind the scene when a user taps on an app icon. How does a developer gain access to the entry point of the application. For this post I will focus on the flow only. If you need to understand how to create your app then follow the simple instructions in this tutorial - Building your first App . Identify MAIN activity When an app launches, the Android OS first looks into AndroidManifest.xml file to identify the MAIN activity. It looks for an activity tag containing intent-filter with name android.intent.action.MAIN. Start the APP Once the MAIN activity class is known, it then creates a new instance and calls onCreate(Bundle savedInstanceState) method. This method is the entry point to the application. Show the APP This is typically done by specifying the elements that a developer wants to display in a layout file stored inside res/layout subdirectory. Android makes it easy to re...