hi Andreas,
No need for a plugin, this line of code in my single.php file does it:
<div class=”navigation”>
<?php previous_post_link(‘«%link’) ?> ::: <?php next_post_link(‘%link »’) ?>
</div>
The “:::” part is just my customization, you can put whatever you like there to separate your navigation links.
For more info, I created my theme from the tutorial and files provided here:
https://www.wpdesigner.com/2007/02/19/so-you-want-to-create-wordpress-themes-huh/