1.What is Servlet? How its works in Struts application?can anyone explain me?
2. Use of serialization? difficult to understand whats the use?
3. Web.XML and struts.config.XML differences between these and how it works?
These questions are a lot like "how does my app work". You are going to need to get a book to learn the basics. Or read the Struts tutorial in detail.
As a teaser:
1) A servlet is provided by Struts as the central dispatcher.
2) Serialization stores forms to disk if the session gets too big
3) web.xml tell your server how to find struts. The struts config tells struts where to find your actions.