User Documentation Components are a type of Extension.
Components are the main functional units of Joomla! they can be seen as mini-applications. An easy analogy would be that Joomla! is the operating system and the components are desktop applications. The content of a component is usually displayed in the center of the main content area of a template (depending on the template).
Most components have two main parts: an administrator part and a site part. The site part is what is used to render pages of your site when they are requested by your site visitors during normal site operation. The administrator part provides an interface to configure and manage different aspects of the component and is accessible through the Joomla! administrator application.
Installing Components
Joomla! comes with a number of core components, like the content management system, contact forms and Banners. More components can be found in the Joomla! Extensions Directory. If you want to learn how to add a component to your Joomla! installation, read more about Installing an extension here.