Heading has main 6 in HTML.<h1>,<h2>,<h3>,<h4>,<h5> and <h6>.<h1> heading comes at the top which represents Head of HTML documents.The higher the heading level number,the <h6> tag defines the least important heading in the document.Text size depends on the number of heading.
<h1>Heading 1</h1>
<h2>Heading 2</h2>
<h3>Heading 3</h3>
<h4>Heading 4</h4>
<h5>Heading 5</h5>
<h6>Heading 5</h6>
Output:-

One more example:-
<!DOCTYPE html>
<html>
<head>
<title>Document</title>
</head>
<body>
<h1>This is Main Heading.</h1>
<h2>This is First sub Heading.</h2>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Iure, possimus?</p>
<h3>This is second sub heading.</h3>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit.</p>
</body>
</html>
Output:-
