QUICK START
Prerequisites for this are knowledge about Acl and Controllers.
This tutorial shows you the required steps to create a menu item that shows a custom ExtJS class (based on Ext.Panel)
Create Ext.Panel based class
Ext.ns('Example');
Example.Foo = Ext.extend(Ext.Panel,
{
    initComponent : function()
    {
        console.log(this.testParameter); //passed by indexAction
        this.html = 'foobar';
        Example.Foo.superclass.initComponent.call(this);
    }
});
Ext.reg('example.foo', Example.Foo);
Create Controller
class Example_FooController extends Kwf_Controller_Action
{
    public function indexAction()
    {
         //pass any parameters that will end up in Panel config
        $this->view->testParameter = 123;
        $this->view->xtype = 'example.foo'; //refer to xtype registered with Ext.reg()
    }
}
also see start controller
Create Menu Entry in Acl that links to new controller
$this->addResource(new Kwf_Acl_Resource_MenuUrl('example_foo',
                array('text'=>trl('Foo'), 'icon'=>'user.png'),
                '/example/foo'));