This is the code for the guide: http://extracatchy.net/add-next-previous-post-button-genesis-theme/

functions.php

<?php
//Do not copy the above php tag. 

function ec_custom_post_navigation()
{
?>
    <div class="prev_next">
        <div class="nav_left">
            <span class="prev">Previous Post</span> <?php previous_post_link('%link', '%title'); ?>
         </div class="nav_right">
        <div>
            <span class="next">Next Post</span> <?php next_post_link('%link', '%title'); ?>
        </div>
    </div>
<?php
}
add_action('genesis_after_entry', 'ec_custom_post_navigation', 2);