Go to wp-admin / Appearance / Menus
Click the plus to add a new menu to WordPress. Name it.
If you premium theme support the new menus you will have a Theme Locations box. In the box you can use the drop down to assign your new menu to a location.
You can add custom link by entering the complete url and a title
Simple, select a page and press add and/or select a category and press the add button.
You can then drag and drop the links around. Finish by pressing the save button.
WordPress 3.0 Menus is a great new feature. Once you get the hang of menus you will wonder how you ever go along without them.
