Here is the code we can use to display related posts.
<?php
//for use in the loop, list 5 post titles related to first tag on current post
$tags = wp_get_post_tags($post->ID);
if ($tags) {
echo 'Related Posts';
$first_tag = $tags[0] -> term_id;
$args = array (
'tag__in' => array($first_tag),
'post__not_in' => array($post->ID),
'showposts'=>5,
'caller_get_posts'=>1
);
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) {
while ($my_query->have_posts()) : $my_query->the_post();
?>
<p>
<a href="<?php the_permalink() ?>"
rel="bookmark"
title="Permanent Link to <?php the_title_attribute(); ?>">
<?php the_title(); ?>
</a>
</p>
<?php
endwhile;
}
}
?>
Credit: WP Support
functions posts related wp_get_post_tags
