The H1 tag is the designation given to headlines on a page. The title tag is what appears on the browser, but the heading 1 (h1) tag appears directly on the page. Think of it as the headline for what is to follow. This is an important element of a page and why you should, if possible, include some of your keywords in the H1 tag.
The H2 tags and lower designations are usually like subheadings on a page. Again these are a good place to include keywords, provided it can be done in a manner that isn't awkward. These subheadings are also a good way to attract a reader's attention and should involve information they are looking for. Readers in hurry and only scanning a page will look at these elements first.
