Theme Modularity and clickable featured images

Hello,

I maintain several website like https://siebeswart.nl and I’d like to understand how to make the featured images clickable. (Right under the slideshow)

I finally found some something in the code , but I don’t want the the_permalink but the extern link attached to the featured picture.
Where can I find it? What’s it called? Or is it too complicated?

The series of category posts just let me click and open the post. I want to skip that step while clicking on the pic. The pic is <?php the_post_thumbnail(); ?> without a link.

<?php while ($cat_query->have_posts()) : $cat_query->the_post(); ?>
		<h3 class="sub"><a href="<?php echo get_category_link($category);?>" title="<?php printf(__('More in %s','gpp_i18n'),get_category($category)->name); ?>"><?php echo get_category($category)->name; ?></a></h3>
		<?php the_post_thumbnail(); ?>
		<h6><a href="<?php the_permalink() ?>" rel="bookmark" title="<?php printf(__('Permanent Link to %s','gpp_i18n'),the_title_attribute('echo=0')); ?>"><?php the_title() ?></a></h6>
		<p class="byline"><?php the_time(__('M d, Y', 'gpp_i18n')) ?> | <?php comments_popup_link(__('Discuss','gpp_i18n'), __('1 Comment','gpp_i18n'), _n('% Comment', '% Comments', get_comments_number(), 'gpp_i18n')); ?></p>
		<p><?php echo substr(get_the_excerpt(),0,100); ?>&hellip;</p>
	<?php endwhile;?>

Thanks!
Elz