How does Struts 1 work?

In my previous projects, I have been using Struts 1 (http://struts.apache.org/) extensively. Although it is an old JEE framework, this framework is still very useful in helping me to understand how Java web-application work.

Here are some of important points about Struts 1 based on my experiences:
1. Struts is MVC framework
2. Main components of Struts
    - Struts-controller
    - ActionForm
    - Action class
    - Command class
3. Big picture of using Struts
4. Simple Struts application


1. Struts is MVC framework
MVC (Model View Controller) is a design pattern that can help us to structure web-application. 'Model' is the data, 'View' is the screen which we are used to show the data to user and 'Controller' is portion which handle all business logic and screen flow.