Simply add the code below to your theme’s functions.php file:

    add_theme_support( 'menus' );


And use this code to insert the menu into your template file:

    <?php wp_nav_menu( array( 'sort_column' => 'menu_order', 'container_class' => 'menu-header' ) ); ?>

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

How to enable Custom Navigation Menus in WordPress 3.0

Like the custom background, header image, and post thumbnails, the custom navigation menus also needs to be enabled through your theme’s functions.php file.

Using Custom Menus in WordPress using PHP

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