To begin the learning process you may want to start with a tutorial or a book.

I recommend to start with the official tutorial for beginners provided by Google.

You can find the tutorial here.

Or you can even follow a book. Here are the 2 books that most people recommend :

  1. Android Programming Second Edition by The Big Nerd Ranch Guide ( Pdf | Amazon )
  2. Hello Android Fourth Edition by Ed Burnette ( Amazon )