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
The banner module is used to display the banners that are managed by the banners component in the site administrator. Help.
This Module allows you to create your own HTML Module using a WYSIWYG editor.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.
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!. 
