Header tags are the H1-H6 tags that give text larger font and prominence. In a well-built site, they are used to give the page structure thus showing both human visitors and search engines what the site is about. By doing so, visitors will better understand the pages and your site will be boosted in search engines.
A good site pulls visitors in with headers that show what the site offers and how to navigate it. This is done by highlighting keywords and topics with header tags. Since most people will quickly move to the next site if they do not see what they page they are on is about quickly, the structure headers add to your site is critical in retaining visitors.
In the same way, search engine algorithms give more weight to words between header tags. While this varies with the search engine and some doubt their effectiveness, if header tags are not abused, they can only help with search engine rankings.
The H1 header tag has the largest font and carries the most weight with search engines. Use it to highlight the most important keywords and themes on each page. Since the font is too large in most situations, you may want to set it to a smaller size using Cascading Style Sheets (CSS). To avoid penalties with search engines, do not use it more than once per page. Use H2-H6 (which are progressively lower in importance) tags to introduce other section headings as needed.
While header tags should contain keywords, do not “stuff” them with keywords and make sure they read as naturally as possible. Doing otherwise can penalize your page with both readers and search engines.
Since link anchor text (the link text that is visible to readers on your site) can also help you on SERP (search engine result pages), you may sometimes want to include your header tag as anchor text. Simply put the header tags on either side of the anchor text.
Bolded and underlined text can also sometimes carry more weight with search engines while outlining your site to readers. These can be used independently or with some combination of header tags and link anchor text.
With the advantages they offer in presenting your site to readers and search engines, header tags should be carefully planned out to give your site optimal advantage.