An extension is a software package that extends your Joomla! installation in some way. A small selection of extensions is included with the default Joomla! installation but many more are available from the Joomla! Extensions Directory.
What are Joomla components?
A component is a kind of Joomla! 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.
How do you components are added in Joomla?
To install a component in Joomla, follow these steps:Choose Extensions→Extensions Manager in any back-end page. Extension Manager opens.In the Upload Package File section, click the Choose File button to browse to and select the component file on your hard drive. Click the Upload File & Install button.