Does anybody understands how to obtain the ORDER number placed in page characteristics? I want only the number and when isn't set, to provide me an specific number (1, or whatever I would like) for those pages who don't put on order page number set.


I am unsure of what you would like...

If you wish to retrieve recption menus_order from the publish/page you should use something similar to

$default = 42;
get_post($id); //you can use any kind of query or use it in the loop
global $post;
if(empty($post->menu_order)) //if not set give the value you want
  $post->menu_order = $default; //note that it won't update the value in the database
echo $post->menu_order;