Hi Mahipal,
Module Pool and Dynpro are the same thing, so if you did not ask what Module pool is I'll assume you know already. Web Dynpro is a different UI technology, which you can find out about here: Web Dynpro ABAP
This doco gives you a great introduction to WDA: Introduction to Web Dynpro ABAP eLearning Series
Web Dynpro also exists in Java flavour, not sure you are interested, but here is the link anyway: Web Dynpro Java
Regards,
Custodio
PS: Next time please do a bit more search