Retrieve value between 2 post

Here is a simple test drive for your question.

// suppose you paste it into a template, eg. page.php or single.php
// I leave out any test or checking, to show to concept
function display_other_post() {
   global $post;

   $current_post_id = $post->ID;
   $other_post_id = 14;

   $other_post = get_post( $other_post_id );
   print_r( $other_post ); // do whatever you need  
}
display_other_post();

In this example, if you run it, no matter what post are you in, you will always display post with ID=14. So I have mentioned that this is a basic method without dynamic capability unless you can get the post ID from your GUI such as adding options in backend, meta value. But it depends on your design and structure first.
So, the first thing is what kind of effect you want to accomplish and how you want to input.