I'm new to ZF and MVC, and after going through documentation I'm unclear how to use Zend_Form. I understand most of the basic structure, but I don't know where to put the code. Some documentation mentions instantiating Zend_Form, then creating a controller to handle it and a view script to display it. I understand controllers and views, but where do I put the Zend_Form instantiating code?

For an example, the Zend_Form official documentation has a section called "15.2.6. Putting it together" on the following page:
Zend Framework: Documentation. I understand the controller and view script code, but where does the first chunk of code go (instantiating Zend_Form and creating username/password elements)? The only place I can think of is the bootstrap file, but I don't think this is the right place.