I am new to Symfony2. Coming from Zend background, I do not see any folder for Models. How do Models and Controllers communicate?

What if I do not want to use Doctrine. Even if I use Doctrine, where will the Models live and how can they communicate with controllers?

Symfony website has some good documentation about symfony2, but it is not on par with the documentation I noticed for symfony1.X .The official documentation does not have what namespaces should be added when using different doctrine methods.
Thanks for the community in advance for the tips.