Displaying a category's description

I’ve been attempting to add my categories descriptions by adding:

<?php
         echo category_description();
?>

To my archive.php file.

But it doesn’t work at all, which I don’t really understand.
Is there a special place within the php.file you’re ought to place it or does the code simply not work for this purpose?

I’m using the theme Minimatic and my modifications is made within a childtheme.
Here’s the link to my site.