In order to get started in Mobile Software Development, the first things you will need to do are:
1. Pick a platform/OS you want to start off with one, then progress to others (you do not have to develop for the phone you yourself have, but it may help in the long wrong)
2. Acquire the tools to develop for your chosen platform most tools are free, however, some are not.
3. Read. Read. Read. Read. Mostly the developers guides and the API references for your platform. They will most likely be located around the same place you found your development tools. They are indispensable. Did I mention that you have to read?
4. Do not skip steps you WILL miss something critical.
5. Ask questions. Use support forums and communities extensively.
6. Be prepared for setbacks, frustrations and tedious repetition of routines. Trial and error is the path to success. Do not get discouraged too easily. Take breaks.
7. Be prepared to actually devote some time to this if you want to be serious. It can be a hobbybut it will still require lots of time to perfect your skill set.
8. If you are afraid of hard work, do not attempt to program. There are worlds of difference between a Hello World and the next million dollar maker.