see this for deets: http://www.wpbeginner.com/wp-themes/how-to-add-custom-navigation-menus-in-wordpress-3-0-themes/

I also added a theme location as well:

in functions.php:

//support WordPress 3.0 menus
add_theme_support('menus');

// This theme uses wp_nav_menu() in one location.
register_nav_menus( array(
'primary' => __( 'Primary Navigation', 'themeName' )
) );

//in header/header-default.php
wp_nav_menu(array('sort_column' => 'menu_order', 'theme_location' => 'primary'));