Joomla is an open-source Content Management System for PHP-based websites. Open-source means its free for anyone to use, so its a great solution especially for smaller organizations who don't have tens of thousands of dollars to develop a webste.
What is a "Content Management System" you ask??
A content management system is software that keeps track of every piece of content on your Web site. Think of it as a library of sorts - it keeps track of all of the content on your website, and stores it all for you. This content can be anything from text to images, to videos, to links. The best part about a good content management system is that typically it requires no technical knowledge to use. If you can use a mouse and type on a keyboard, you're pretty much all set.
There is a lot of documentation on how to use Joomla out on the internet. Here is a good place to start: http://docs.joomla.org/Beginners
We have created a few documents which can help you with details specific to creating and editing articles in the latest version of Joomla.