Header tags used to structure the web page. For example, if need to write content in various level of heading then use below tags to write the text.
<h1> - Most important and top level bigger text
<h2> - if need to write a little smaller text compare to h1 use h2
<h3>, <h4>, <h5>, <h6> - same rule goes here for h3, h4, h5 & h6 is the smallest header text.
create a file called "headers_ex.html" and type the below lines.
<h1>Heading1</h1>
<h2>Heading1</h2>
<h3>Heading1</h3>
<h4>Heading1</h4>
<h5>Heading1</h5>
<h6>Heading1</h6>
save the file and open it in the browser and check the results.