Before beginning with developing the Android application you should have a good knowledge of java. Going through various websites such as
javapoint.com, tutorialspoint.com will definitely help you to learn Java.
So, to develop the Android application you will need an IDE or Integrated Development Environment, there are many IDE’s available which can help with android development such as Eclipse or Android Studio (most preferred).
Developing android application will take lots of time and will require lots of patience. An Android app cannot be developed overnight since the app will require lots of things to taken care of.
When stuck on a problem (which will inevitably happen), turn to Stack Overflow. You may or may not find the solution. If you didn't find the solution explore more as exploring will lead you to know more about android.