After registering your menus, use wp_nav_menu() to inform your theme where to display your menus. You can add this code to a header.php file for displaying the registered header-menu:
wp_nav_menu( array( 'theme_location' => 'header-menu' ) );

BY Best Interview Question ON 28 Feb 2023

Example

wp_nav_menu( array $args = array(
   'menu' => "",
   'menu_class' => "",
   'menu_id' => "",
   'container' => "",
   'container_class' => "",
   'container_id' => "",
   'fallback_cb' => "",
   'before' => "",
   'after' => "",
   'link_before' => "",
   'link_after' => "",
   'echo' => "",
   'depth' => "",
   'walker' => "",
   'theme_location' => "",
   'items_wrap' => "",
   'item_spacing' => "",
) );
// These are the parameters od this function.