Please use the following steps to utilize drupal menu style :

1. Go to Drupal Administer -> Site Building -> Menus (www.YourSite.com/?q=admin/build/menu)

2. Edit an existing menu or create a new one.

3. Go to Drupal Administer -> Site Building -> Blocks (www.YourSite.com/?q=admin/build/block)
4. Place menu into the "Menu" region.

NOTE: the "Menu" region can contain only a single menu, or none.

If this information is not enough you can read more on http://drupal.org/node/102338