Hi Seetha
I agree with Paul... there is a lot of info on SCN itself as well as on google.
Googling gave me this link which can help you understand the standard workflow for PR Release a bit more:
It talks about different workflows, first one being the PR Approval Workflow.
I am sure you would have narrowed down to the standard WF template for this, if not, it is WS00000038. Go ahead and explore that in PFTC and SWDD -> you can find answers to your questions right in the definition of this Workflow. Each Release level will result in a new instance of this workflow.
Regards,
Modak