When the user types the URL ..../main.jsp and the
JSP tags are interpreted and rendered into HTML, that's one request. When the user clicks the submit button, that causes the browser to send another request to the server. Your SubmitAction class reads that request and then forwards to main.jsp, which has access to that request object as it's rendering the HTML to be sent back to the browser.
So, from the time the user first types in the URL to the page being displayed a second time, there are two requests. From the time the user presses the submit button until the page is redisplays, there is one request.
Does that make sense? I hope I haven't added more confusion.