The process of downloading and installing extensions hasn't changed in version 1.6. The Joomla! Extensions Directory (http://extensions.Joomla.org) offers a great overview of the extensions currently available. At the time of writing, more and more extensions are becoming available for Joomla! 1.6. To make sure that the extension you want to download and install is ready for Joomla! 1.6, check for the 1.6 Native label in the Compatibility information for the extension:
To see a list of all extensions that are compatible with Joomla! 1.6, in the Joomla Extensions Directory, click on Advanced Search and select 1.6 Native in the Compatibility drop-down box.
Note
If you're interested in developing extensions for Joomla! yourself, consult http://www.joomla.org/16/features/developer.html. This page contains an overview of technical changes in the software that are relevant to developers and also provides links to several resources about developing...