Hi Amarbhanu

The official documentation for developing modules can be found here: http://doc.silverstripe.org/doku.php?id=creating-modules

If you are new to SS I would reccommend doing the tutorials here: http://doc.silverstripe.org/doku.php

Also http://www.ssbits.com is a site which provides tutorials and code snippets for SS (I only launched it recently so there is not a huge amount on there yet, but expect updates every few days)

Hope that helps

Aram