wordpress how to add thumbnail image to menu code example

Example: wordpress get post thumbnail

<?php 
/* RETURNS a full image resource as: <img class="data..." src="data...">
   ALL parameters are optional. Not needed if you are on WP LOOP
*/
echo get_the_post_thumbnail( $the_query->ID, array( 500, 400) ); 
/* USE get_the_post_thumbnail_url() to get only the image url */
?>