Heading Tags are HTML commands used to highlight the most important parts of a pages content. There are six types of heading tags ranging from H1 to H6. In terms of search engine rankings H1 and H2 tags are most valuable. Their importance is twofold. First, they guide search engine crawlers to the most relevant words on a web page, and secondly, they are used to draw the users attention to particular parts of the content.
Due to the impact heading tags have on both the visitors and search engine rankings it is important to use them appropriately on each web page.
H3 to H6 heading tags can also be used to style a page but have far less importance (if any) for search engine ranking.