The Benefits of HTML Headings
One of the more common text formatting options in HTML is the heading style. In HTML, you gain many advantages to using the heading styles (H1, H2, and so on) to style text that serves as titles or headlines. That's because heading styles are designed to be displayed in relative sizes no matter which text size users set in their Web browsers. When you use headings, H1 is the largest, H2 is the next largest, and so on, decreasing in size through H6. Another benefit to using headings is that search engines generally give priority to keywords that are formatted with the H1 or H2 tags, because the use of a heading tag implies that the text has greater importance on a page.
Because you can redefine any HTML tag with CSS, you can alter the display of heading tags while still enjoying the benefits. You can also combine styles so that text formatted with an H1 tag can appear one way when placed within the sidebar of a page and appear another way when placed within the main content area. That's why many CSS layouts that come with Dreamweaver include styles like #header H1 — because a style with that name redefines text that's formatted with the H1 tag only if it appears within a Div that has the ID "header."
You can apply Heading tags to text by selecting any text on a page and then using the drop-down list in the Property inspector at the bottom of the screen to select a Heading option.