Usando a tag <a></>

O que esta errado aqui:

<h2>CatPhotoApp</h2>
<main>

  <a href="https://freecodecamp.org">Cat Photos   </a>
  
  <img src="https://bit.ly/fcc-relaxing-cat" alt="A cute orange cat lying on its back.">

  <p>Kitty ipsum dolor sit amet, shed everywhere shed everywhere stretching attack your ankles chase the red dot, hairball run catnip eat the grass sniff.</p>
  <p>Purr jump eat the grass rip the couch scratched sunbathe, shed everywhere rip the couch sleep in the sink fluffy fur catnip scratched.</p>
</main>

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).