You can read more about Joomla application and all features of it from the official Joomla website:
http://www.joomla.org
You can also review the official documentation for Joomla from the following link:
https://docs.joomla.org/
The Joomla forum is located on the following link:
http://forum.joomla.org/
The Joomla community portal can be accessed from here:
http://community.joomla.org/translations.html
The Joomla resource directory is located here:
http://resources.joomla.org/en/
You can also search for an extensions for your Joomla website from the following link:
http://extensions.joomla.org/