When the APEX server receives a submit request from a browser, it performs the validations and processes associated with that request. Its final task is to choose a target page to send to the browser. By default, APEX chooses the page that was submitted, but it is possible to specify another page by creating a branch.
You have been able to get this far through the book without needing to use branches because of the ease in which multiple regions can be created on a page and the way that these regions can be conditionally rendered to give the effect of multiple pages. But there are many situations in which an application will ...