Menus provide your site with structure and help your visitors navigate your site. Although they are all based on the same menu module, the variety of ways menus are used in the sample data show how flexible this module is.
A menu can range from extremely simple (for example the top menu or the menu for the Australian Parks sample site) to extremely complex (for example the About Joomla! menu with its many levels). They can also be used for other types of presentation such as the site map linked from the "This Site" menu.