Hi Lorence,
In the page layouts for the essentials theme, you will need to add lines similar to:
$menudata = totara_build_menu();
$totara_core_renderer = $PAGE->get_renderer('totara_core');
$totaramenu = $totara_core_renderer->print_totara_menu($menudata);
and "echo $totaramenu;" where you would like it displayed. Please note that you may also need to have a number of CSS declarations to display correctly.
Kind Regards,
Brian Barnes