Do I put <u1> or do I list things then close it

Tell us what’s happening:
Describe your issue in detail here.

  **Your code so far**
<html>
<body>
  <h1>CatPhotoApp</h1>
  <main>
    <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>
    <section>
      <h2>Cat Lists</h2>
      <h3>Things cats love:</h3> 
      <u1>
    </section>
  </main>
</body>
</html>
  **Your browser information:**

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.3 Safari/605.1.15

Challenge: Step 19

Link to the challenge:

Not <u1> but <ul> (which stands for Unordered List UL). And it requires closing tag as well.