display custom post on separate page

The simplest way is to create Page (maybe call it “All Codes”). Then, you “hijack” that page’s PHP template by creating a PHP file in your theme’s directory called page-all-codes.php (note how the “all-codes” part corresponds to the slug of the Page you created).

You can then use WP_Query to get a list of your posts. Your arguments should look like this – feel free to add more to customize your list (like how you want them ordered etc)

$args = array(
  'post_type' => 'code',
  'posts_per_page' => -1
);

How you use these $args is up to you. The easiest (and in this case, probably not so bad) way is query_posts( $args );.