Sonata is a ecosystem of many bundles, we split them into the following categories: persistence, foundation, feature and libraries. First you should start with the SonataAdminBundle documentation.
The main bundle of Sonata, it includes the main features of a CMS generator.
Official persistence bundles, depends wheter you use Doctrine ORM or another solution you might need different persistence bundle.
Base features that most CMS could need.
Useful features packaged in a bundle to be installed if you need them.
Libraries used by our bundles, but can be also be installed as standalone packages.
General documentation