Answer:
This is a link that allows you to navigate within the same web page.
Step-by-step explanation:
Here's an example:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<a href="#lession1">Lession.1</a><br />
<a href="#lession2">Lession.2</a><br />
<br />
<a id="lession1">Introduction of Lession.1</a>
<p>This is sub topic.1</p>
<p>This is sub topic.2</p>
<br />
<br />
<div id="lession2">Introduction of Lession.2</div>
<p>This is sub topic.1</p>
<p>This is sub topic.2</p>
<br />
<br />
</body>
</html>