Understanding WordPress 3.X Menus (Video)
Custom menus allow you to extend your site’s capabilities with easy to use components such as category and recent post listings or even a calendar.
You customize menus as follows:
1. Click on Menus in the Appearance module
2. Enter Menu Name then click Save Menu

3. Select your new Menu Name from the drop-list in the Theme Locations section
4. Add links to the menu using the Custom Links, Pages or Categories modules
5. Re-order the menu items as you like, then press Save Menu

Enjoy!

