Struts can be a little confusing, especially if you come from a Servlet/JSP background.
The key to Struts is ActionClasses (the front controller), the config file, where navigation, actions, and links are mapped, and Form beans, that help with validation. Those are the basics, and you build from there.
Free Multimedia Tutorial on Struts Development I have a few tutorials on Struts on my website. They'll demonstrate the basics. I highly recommend you check them out, just to get an idea on what is going on with a struts app. From there, hunker down with a good book.
Cheers!
-Cameron McKenzie