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.
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 and edited from the front end, making content the easiest component to use to create your site content. Help
Joomla! 2.5 offers two search options.
The Basic Search component provides basic search functionality for the information contained in your core components. Many extensions can also be searched by the search component. Help
The Smart Search component offers searching similar to that found in major search engines. Smart Search is disabled by default. If you choose to enable it you will need to take several steps. First, enable the Smart Search Plugin in the plugin manager. Then, if you are using the Basic Search Module replace it with the Smart Search Module. Finally, if you have already created content, go to the Smart Search component in your site administrator and click the Index icon. Once indexing of your content is complete, Smart Search will be ready to use. Help.