In general, the link that Dyrborg provided is a good starting point:
stackoverflow.com/questions/9293329/where-is-main-in-android
The general answer to your question is that in Android development, there is no main.java or public static void main(string[] args) entry point. Although there is a single Application class which Android uses to manage your application, you shouldn't access it until you understand more general concepts of an Android application lifecycle. What you want to look into, and your first starting point, is your main Activities methods. In particular onCreate(), onStart(), onResume() and onPause().
I suggest you take the time to read the Android tutorials, in particular this article on Activities, which are the main entry points you need to be concerned with initially.
http://developer.android.com/training/basics/activity-lifecycle/index.html