how do I create submenus in my module?
I've pasted a sample code below. Hope that helps.     

 function hook_menu() {
      $items = array();

      $items['demo'] = array(
      //other code here
      ); 

      $items['more-demos'] = array(
      //other code here
      );

      $items['more-demos/extra-demo-1'] = array(
      //other code here
      );

      $items['more-demos/extra-demo-2'] = array(
      //other code here
      );

      return $items;
    }