Web applications frameworks support the development of Java web applications for years. They aim to alleviate the overhead associated with common activities like internationalization, automated form validation, caching, Ajax, and more.
Only recently have they started playing an important role in PHP, more specifically since the release of the PHP 5.
Symfony is fully documented and has a nice step-by-step tutorial covering all its features: Askeet - symfony Advent Calendar. With the release of symfony 1.0, Francois Zaninotto has seized the opportunity to post a beginner’s symfony tutorial at Sitepoint.
Start now using it and make your applications faster, better, and Web 2.0 ready.