HI Devang,
I strongly recommend that you start by reading RFC2581, which documents the four algorithms used by TCP for congestion control.
Here's a link to it:
http://www.ietf.org/rfc/rfc2581.txt
Once you have done that, you can then ask more specific questions about things you do not understand .
Hope that helps - pls rate the post if it does.
Paresh