This is a reference to be used for Model rule validation and is compiled from the Yii documentation and code. The purpose is to have all the information gathered in one place instead of scattered. This reference is not an intro.
See The Definitive Guide to Yii, Declaring Validation Rules for a tutorial.
So you want to use CForm (form builder), but need to preload dropdowns in a form? It's simpler than it seems.
You got your CFormModel, CForm and the actual Form, right?
Let's say you have the typical State -> City dependent dropdowns, so you would want to load the from with the State and City selected.