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.
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.
The users extension lets your site visitors register, login and logout, change their passwords and other information, and recover lost passwords. In the administrator it allows you to create, block and manage users and create user groups and access levels. Help
Please note that some of the user views will not display if you are not logged-in to the site.