Heading tags were originally meant to break up text blocks and make it easier to find appropriate sections.

Search engines use them to add value to your page and this can benefit relevance in your ranking.

They are coded.

<h1>This is what my page is about</h1>. It should be similar to your Page title.

It would be confusing if your page title is <title>H1 Tags</title> and your H1 tag is <h1>Cruises around the Baltic</h1>.

The coding for H1 tags is usually with the largest font on your webpage.

H1 and h2 heading tags

It’s also important to be able to format other sections of your post as subheadings (h2).

Where an h1 tag is the subject of your page, using h2 tags enables you to specify subsections.The “Long foldover skirt,” “Tiered peasant skirt” and “Ponte pleated skirt” sections are all formatted using h2 tags.

Do not overdo it.

Once or twice for H1 tags at most is OK but if you abuse it, Google has an algorithm to counter the effect.

You can use H2, H3 down to H6 and there is no real limit.

But do not make everything h tags and have no ordinary text.

Matt Cutts 2009