Given below are a few references to Android apps development:
http://developer.android.com/google/index.html (http://developer.android.com/google/index.html)
http://developer.android.com/guide/index.html (http://developer.android.com/guide/index.html)
http://www.sitepoint.com/getting-started-with-android-library-projects-part-1/ (http://www.sitepoint.com/getting-started-with-android-library-projects-part-1/)
Create Your Developer page:
https://support.google.com/googleplay/android-developer/answer/6226441 (https://support.google.com/googleplay/android-developer/answer/6226441)
Application licensing:
http://developer.android.com/google/play/developer-api.html (http://developer.android.com/google/play/developer-api.html)