function mymodule_menu() {
  $items['page-example'] = array(
    'title' => 'Page callback example',
    'page callback' => 'my_page_callback',
    'access arguments' => array('access content'),
  );
  return $items;
}

function my_page_callback() {
  return array(
    '#theme' => 'html_tag',
    '#tag' => 'div',
    '#attributes' => array(),
    '#value' => 'Hello world',
  );
}