The Joomla! content management system lets you create webpages of various types using extensions. There are 5 basic types of extensions: components, modules, templates, languages, and plugins. Your website includes the extensions you need to create a basic website in English, but thousands of additional extensions of all types are available. The Joomla! Extensions Directory is the largest directory of Joomla extensions.
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 such as Menus, Redirection, and the extension managers.
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 24 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.
Content modules display article and other information from the content component.
These modules display information from components other than content and user. These include weblinks, news feeds and the media manager.
Navigation modules help your visitors move through your site and find what they need.
Menus provide your site with structure and help your visitors navigate your site. Although they are all based on the same menu module, the variety of ways menus are used in the sample data show how flexible this module is.
A menu can range from extremely simple (for example the top menu or the menu for the Australian Parks sample site) to extremely complex (for example the About Joomla! menu with its many levels). They can also be used for other types of presentation such as the site map linked from the "This Site" menu.
Breadcrumbs provide users with information about where they are in a site.
Templates give your site its look and feel. They determine layout, colours, typefaces, graphics and other aspects of design that make your site unique. Your installation of Joomla comes prepackaged with three front end templates and two backend templates. Help
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. Help
These are my photos from parks I have visited (I didn't take them, they are all from Wikimedia Commons).
This shows you how to make a simple image gallery using articles in com_content.
In each article put a thumbnail image before a "readmore" and the full size image after it. Set the article to Show Intro Text: Hide.