Support for the Joomla! CMS can be found on several places. The best place to start would be the Joomla! Official Documentation Wiki. Here you can help yourself to the information that is regularly published and updated as Joomla! develops. There is much more to come too!
Of course you should not forget the Help System of the CMS itself. On the topmenu in the Back-end Control panel you find the Help button which will provide you with lots of explanation on features.
Another great place would of course be the Forum . On the Joomla! Forum you can find help and support from Community members as well as from Joomla! Core members and Working Group members. The forum contains a lot of information, FAQ's, just about anything you are looking for in terms of support.
Two other resources for Support are the Joomla! Developer Site and the Joomla! Extensions Directory (JED). The Joomla! Developer Site provides lots of technical information for the experienced Developer as well as those new to Joomla! and development work in general. The JED whilst not a support site in the strictest sense has many of the Extensions that you will need as you develop your own Web site.
The Joomla! Developers and Bug Squad members are regularly posting their blog reports about several topics such as programming techniques and security issues.
Joomla! Documentation can of course be found on the Joomla! Official Documentation Wiki. You can find information for beginners, installation, upgrade, Frequently Asked Questions, developer topics, and a lot more. The Documentation Team helps oversee the wiki but you are invited to contribute content, as well.
There are also books written about Joomla! You can find a listing of these books in the Joomla! Shop.