The Yii documentation states:

An application module may be considered as a self-contained sub-application that has its own controllers, models and views and can be reused in a different project as a whole. Controllers inside a module must be accessed with routes that are prefixed with the module ID.

So practically, a module can be handled just as an application, with only minor differences.

Supposing you were having a custom component 'foo' in your application:

return array(
    'basePath'=>dirname(__FILE__).DIRECTORY_SEPARATOR.'..',
    'preload'=>array('log'),
    'import'=>array(
        'application.models.*',
        'application.components.*'
    ),
    'components'=>array(
        'db'=>array(
        ),
        //right down here:
        'foo' => array(
            'param1' => 'val1'
        )
    ),

And you need to move it inside a module called 'bar':

return array(
        'basePath'=>dirname(__FILE__).DIRECTORY_SEPARATOR.'..',
        'preload'=>array('log'),
        'import'=>array(
            'application.models.*',
            'application.components.*'
        ),
        'components'=>array(
            'db'=>array(
            )
        ),
        'modules' => array(
            'bar' => array(
                'components' => array(
                    'foo' => array(
                        'param1' => 'val1'
                    )
 
                )
            )
        )
    //...

Now instead of using the component as usual:

Yii::app()->foo

You need to call it like this from within the module:

Yii::app()->controller->module->foo

As you can see, your module is indeed just another application, and you can configure any parameters as you'd do with your "root" application. The only organizatory differences are:

• a module has a module "entry point", the FooModule which extends CWebModule, whereas the root application is bootstrapped by the framework itself, starting with your entry script (index.php)
• the application's SiteController is called inside a module DefaultController