you can create mobile application  based on your requirement or learning purpose.before that you have to learn Java programing language because all mobile based application should be consider with java programming class .the moble app code same like java programming .if you know java means you can easily understand mobile apps code.after java basics learning you should download simple mobile apps code and understand that how they using the code and how it works.
  after that u can start the simple mobile apps code
  please download eclipse software for mobile apps creation .it shoud be useful for begginer to master.
  note : if u have any doubt u can ask us we will help You .