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.
All components are also used in the administrator area of your website. In addition to the ones listed here, there are components in the administrator that do not have direct front end displays, but do help shape your site. The most important ones for most users are
The media manager component lets you upload and insert images into content throughout your site. Optionally, you can enable the flash uploader which will allow you to to upload multiple images. Help
The extensions manager lets you install, update, uninstall and manage all of your extensions. The extensions manager has been extensively redesigned, although the core install and uninstall functionality remains the same as in Joomla! 1.5. Help
The menu manager lets you create the menus you see displayed on your site. It also allows you to assign modules and template styles to specific menu links. Help
The global configuration is where the site administrator configures things such as whether search engine friendly urls are enabled, the site meta data (descriptive text used by search engines and indexers) and other functions. For many beginning users simply leaving the settings on default is a good way to begin, although when your site is ready for the public you will want to change the meta data to match its content. Help
The banners component provides a simple way to display a rotating image in a module and, if you wish to have advertising, a way to track the number of times an image is viewed and clicked. Help
The redirect component is used to manage broken links that produce Page Not Found (404) errors. If enabled it will allow you to redirect broken links to specific pages. It can also be used to manage migration related URL changes. Help