As a part of his demo (presented at a local user group meeting) Bradley Holt, not having enough time to squeeze in all of the content he wanted, has started off a series of posts to his blog about the Zend Framework and the specific areas that make it up. His first article is about the front controller.
Like many other frameworks, Zend Framework provides an implementation of the Front Controller pattern. This means that all HTTP requests can be sent through a centralized point. This allows you to take advantage of Zend Framework's routing and Model-View-Controller (MVC) components, if you so choose.
He talks about where the Zend Framework places this controller and what their version of it contains - constant definitions, loading paths and the creation of a Zend_Application instance that's called to do the real work. He also includes a few helpful tips on common problems you might come across when setting up your application.