Overview
All the template functions (get_field, the_field, etc) can be used to load values from another post, however, a second parameter is required to target the post.
Each post has a unique ID which can be found in the URL when editing, or found via code such as $post->ID.
Examples
Display a field
This example will display a field value from the post with an ID of 123.
<p><?php the_field('field_name', 123); ?></p>Retrieving a field
This example will retrieve a field value from the post with an ID of 123.
<?php
$variable = get_field('field_name', 123);
// do something with $variable
?>Retrieving a field from post object
This example will retrieve a field value from a previously found $post object.
<?php
$variable = get_field('field_name', $post->ID);
// do something with $variable
?>Working with the Repeater Field
Note that when inside of a have_rows loop, you do not need to use the $post_id parameter for any sub field functions (get_sub_field, the_sub_field)
<?php if( have_rows('repeater', 123) ): ?>
<ul>
<?php while( have_rows('repeater', 123) ): the_row(); ?>
<li><?php the_sub_field('title'); ?></li>
<?php endwhile; ?>
</ul>
<?php endif; ?>