Registering and displaying custom menu in WordPress

add to your function.php file the following code :

// my custom menu
function mymenu_get_menu_items($menu_name){
    if ( ( $locations = get_nav_menu_locations() ) && isset( $locations[ $menu_name ] ) ) {
        $menu = wp_get_nav_menu_object( $locations[ $menu_name ] );
        return wp_get_nav_menu_items($menu->term_id);
    }
}

then in a template file in a place where the menu need to be displayed :

$menu_items = yourmenu_get_menu_items('your-menu-location'); // replace your-menu-location by desired location

if(isset($menu_items)) {
echo '<ul>';
      foreach ( (array) $menu_items as $key => $menu_item ) {
         echo '<li><a href="'.$menu_item->url.'" title="'.$menu_item->title.'">'.$menu_item->title.'</a></li>';
      }
 echo '</ul>';
}