Extensions
Users
The users extension lets your site visitors register, login and logout, change their passwords and other information, and recover lost passwords. In the administrator it allows you to create, block and manage users and create user groups and access levels. Help
Please note that some of the user views will not display if you are not logged in to the site.
Who's Online
The Who's Online Module displays the number of Anonymous Users (e.g. Guests) and Registered Users (ones logged in) that are currently accessing the Web site. Help
Wrapper Module
This module shows an iFrame window to specified location. Help
News Feeds
News Feeds (com_newsfeeds) provides a way to organize and present news feeds. News feeds are a way that you present information from another site on your site. For example, the joomla.org website has numerous feeds that you an incorporate on your site. You an use menus to present a single feed, a list of feeds in a category, or or a list of all feed categories. Help
Breadcrumbs Module
Breadcrumbs provide a pathway for users to navigate through the site. Help
Subcategories
Components
Components are larger extensions that produce the major content for your site. Each component has one or more "views" that control how content is displayed.In the Joomla! administrator there are additional extensions suce as Menus, Redirection, and the extension managers.
Modules
Modules are small blocks of content that can be displayed in positions on a web page. The menus on this site are displayed in modules. The core of Joomla! includes 17 separate modules ranging from login to search to random images. Each module has a name that starts mod_ but when it displays it has a title. In the descriptions in this section, the titles are the same as the names.
Templates give your site its look and feel. They determine layout, colors, type faces, graphics and other aspects of design that make your site unique. Your installation of Joomla comes prepackaged with four templates. 
Plugins are small task oriented extensions that enhance the Joomla! framework. Some are associated with particular extensions and others, such as editors, are used across all of Joomla!. Most beginning users do not need to change any of the plugins that install with Joomla!.