An element starts with its opening tag (<section> in this case) and ends with its closing tag (</section>) in this case. So when you are asked to add a new section below, or after the existing section, that means to add it after the entire section element, which means both the opening and closing tags. Right now you have nested the existing section in a new section.
Restart the step to get the original HTML back. You should see the following:
<section>
<h2>Cat Photos</h2>
<!-- TODO: Add link to cat photos -->
<p>Click here to view more <a target="_blank" href="https://freecatphotoapp.com">cat photos</a>.</p>
<a href="https://freecatphotoapp.com"><img src="https://cdn.freecodecamp.org/curriculum/cat-photo-app/relaxing-cat.jpg" alt="A cute orange cat lying on its back."></a>
</section>
Do you see how this section element starts with an opening <section> tag and ends with a closing </section> tag. Those two tags, plus everything in between them, make up this entire section element. So to add a new section element below, or after this one means to add the new section after all of this, after the entire section element.
Thanks so much, it worked. You really helped me, I wish you can be my personal teacher as I go along this course, because I will need a mentor to finish this course.