I am creating a Windows 8 RT app and would like to run the app itself as soon the Windows 8 gets started..
How do I achieve this?
Short answer
You can't. It is up to the user which apps to launch and when to launch them. This is fundamental to the Windows 8 app philosophy.
Longer answer
You could probably achieve your goals in a better way than this. If you can update your answer with an overview of what you want to achieve, we may be able to suggest alternatives.