I have managed to register a new menu (the blue menu at the top of the browser window) and show it on my website by adding the following to header.php above the #wrapper div:
<div id="eCommerceNav" role="navigation"> <?php wp_nav_menu(array( 'container_class' => 'menu-eCommerce', 'theme_location' => 'ecommerce' )); ?> </div>
I want the menu to sit flush at the top and full width of the browser window. Please see my screen shot of how I would like it to look.
I am using a child theme.