In Joomla!, articles are segmented by sections and categories. In Joomla! 1.5, you had the ability to lay out your site via this section and category segmentation.
In Joomla! 1.6, the sections are gone in favor of multiple nested categories setup. In other words, it can look something like this:
This enables administrators to set up unlimited levels of nested categories. You can control access to each of the various levels using the new ACL system in Joomla! 1.6.
There is very little work to do in preparation for this, except to figure out what your categories are. Don't worry if you aren't sure of the ...