Hi Sangu,
The place to a to learn about programming in Moodle is Moodle Docs, Developer section, programming guidelines. You will find general information there for developers. You should alos do a search in Moodle Docs for any articles on previously developed whiteboards. I know there has been at least three whiteboard modules developed for Moodle, and you may want to ask yourself, "Is a whiteboard module needed for Moodle?" Maybe the previous ones are just fine, or maybe they are flawed and need a new person (like you) to work on it. You may want to
Moodle itself is programmed in PHP, but there are some limited cases where other languages have been used partially in the process.
Hope this helps,
Don