Content to be finalized. First draft
Struts is built on a MVC architecture, which means the application is arranged into 3 primary types of code. These are know as a Model, View and Controller. The Model defines the structure of your data being processed. The View defines everything that a end user can see. The controller take the model as submitted from the page, performs business logic on the data, then decides what view should be responsible for displaying the result.
I will not spend any more time talking about the architecture of struts. If you would like to have more information on that topic, I suggest going to the official website.