Extensions
Banner Module
The banner module is used to display the banners that are managed by the banners component in the site administrator. Help.
Contacts
The contact component provides a way to provide contact forms and information for your site or to create a complex directory that can be used for many different purposes. Help
Content
The content component (com_content) is what you use to write articles. It is extremely flexible and has the largest number of built in views. Articles can be created an edited from the front end, making content the easiest component to use to create your site content. Help
Custom HTML Module
This Module allows you to create your own HTML Module using a WYSIWYG editor. Help
Editors
Editors are used thoughout Joomla! where content is created. TinyMCE is the default choice in most locations although CodeMirror is used in the template manager. No Editor provides a text box for html content.
Default on:
- CodeMirror Help
- TinyMCE Help
- No Editor Help
Default off:
- None
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!.