Need more example to show like the demo

Hi, can you just try putting this code into your theme's functions.php file?

add_action( 'mb_relationships_init', function() {
    MB_Relationships_API::register( array(
        'id'   => 'posts_to_pages',
        'from' => 'post',
        'to'   => 'page',
    ) );
} );

You'll see meta boxes "Connected From" and "Connects To" for posts and pages. It's the most basic usage.

Please try it.