Understanding the concept of prefix paths and overriding existing plugins will help you with your understanding of many components within the framework. Plugins are used in a variety of places:
Zend_Controller_Action: action helpers.
Zend_Form: elements, filters, validators, and decorators.
Zend_View: view helpers.
And several more places, besides. Learn the concepts early so you can leverage this important extension point in Zend Framework.
We'll note here that