Joomla is an open source content management system (CMS) that makes it easy to build and manage websites. It allows non-technical users to add and edit content without needing HTML skills. Some key features include a user-friendly interface, built-in professional features, and hundreds of free and commercial extensions. Major organizations like the UN, MTV, and Harvard use Joomla for their websites. The document provides an overview of why to use Joomla, how to install it, and how to organize and manage content once installed.