Hi Dipanjan,
There isn't really a formal registration process, but registering at
http://bugs.wireshark.org/ is a good place to start. As for "tasks" - there isn't a formal list of mandatory activities (but there is a wishlist on the wiki, which might be vaguely interesting); and things are fairly ad-hoc - you just think "I'd like to implement feature X", do it, and post a diff on the bug tracker.
If you think that you're going to do something that conflicts with what others are doing, then it's a good idea to ask on this list, first.
I hope that helps - and welcome aboard!
Tyson.