Template file snippet to add ACF fields to a FooGallery template in order to display a gallery description. See this post:

default-gallery-with-description.php

//'foo_gallery_description' is the slug of the custom field. Second parameter is the current foogallery id.
<?php if(get_field('foo_gallery_description', $current_foogallery->ID)){ ?>
  <div class="gallery-desc">
    <p><?php the_field('foo_gallery_description', $current_foogallery->ID); ?></p>
  </div>
<?php } ?>