In my daily development, the h1~h4 I use most often. Today, VeVb.com still recommends that you use both h1 and h6.
The html tag has a special tag processing title on the page. They are h1, h2, h3, h4, h5 and h6. Like feudal society, h1 is the omnipotent monarch and h6 is the lowest-level people.
<h1>Main title, written here</h1>
<h6>Title, written here</h6>
<!doctype html public -//w3c//dtd xhtml 1.0 strict//en
http://www.w3.org/tr/xhtml1/dtd/xhtml1-strict.dtd>
<html>
<head>
<title>My first web page - VeVb.com</title>
</head>
<body>
<h1>My first web page - VeVb.com</h1>
<h2>What is this</h2>
<p>Simple web pages combined with html</p>
<h2>Purpose</h2>
<p>Learn HTML</p>
</body>
</html>
Note that the h1 tag can only be used once on a page - assuming it is the main title of this page, it should not be used multiple times (equivalent to the title of an article, you can have a sub-topic, but you won't use two parallel titles, right? - Translator's note VeVb.com).
However, h2 to h6 can be used as many times as you need, but they should be used in order according to the design intention. For example, h4 should be the subtitle of h3, h3 should be the subtitle of h2, and so on.