Joomla menus define how the user will access the content of a site. Presentation, however, is defined by the interaction of three elements used by the system: templates, modules, and components. Joomla is incredibly flexible because each of these elements can be modified or replaced.
Joomla! Overview, Part II - How is Joomla! organized?
When first approaching Joomla, one of the hardest things to understand is how the system itself is organized. It's straightforward enough to add an article, but how do you determine where on the site that article will be displayed? The answer to this question is menus.
If you're a graphic designer and haven't heard of Joomla, you can dramatically increase your web design power and possibilities of employment by learning it. Joomla is a free, open-source, Content Management System (CMS). Joomla lets someone design, develop, and deploy a complete web site without programming a single line of HTML. Better still, you can maintain a Joomla site through the web-based Administrator interface from anywhere.