Headings are created with a <hn> tag, in which there is a number between 1 and 6

The table below shows headings as normally displayed from larger to smaller.

Why use Heading Tags?

Heading tags are used by search engines to identify words which are more important than the rest of the page text. The headings should sum up the topic of the page, so they are counted as important keywords.  Therefore keywords should be incorporated into Headings as much as possible.

Normally there would be no need to use 6 different styles of headings. Extensive SEO only uses the first three and then uses CSS to style the headings in differnt ways.

For exemple: Lets look at the code for the logo of Extensive SEO at the top of the page.

This is the HTML code for that logo:

 <div id="logo">
          <h1><a href="">Extensive <i>SEO</i></a></h1>
          <h2><i>Search Engine Optimization</i>techniques and Strategies for<i>ASP.NET and HTML.</i></h2>
         </div>

And the corrisponding CSS:

#logo {
float: left;
height: 87px;
color: #36393D;
padding-right: 0px;
padding-left: 5px;
padding-bottom: 0px;
padding-top: 0px;
}
#logo h1 {
padding: 3px 0 0 0;
}
#logo h2 {
left: 25px;
position: relative;
}
#logo a {
text-decoration: none;
}

The logo did take a good amount of CSS to style in a way that enhances usability and appearence but the end result when looking at the HTML code it is very compact and optimized for SEO for two reasons.  The first is the use of heading tags in the logo and secondly is that the Keywords are italicized to add forther emphasis.