Header Tag in HTML:

<h1></h1>
<h2></h2>
<h3></h3>
<h4></h4>
<h5></h5>
<h6></h6>

1.<h1></h1> means:
  It shows the letters in large font face.For an example <h1>Header</h1>

2.<h2></h2> means:

 It shows the letters in large font face but letter size has been reduced in <h1> tag.
For an example <h2>Header</h2>