H# tags stand for Headlines and that’s exactly what they should be used for on a page.
Table of Contents
H1 Tag is the Most Important Keyword Topic Indicator
H1 is the Most Important Phrase or Sentence on Your Page
If you think of a Web page as an outline, the H1, H2, etc. heading tags serve to divide the page into sections. Your most important headline is your H1 headline. This generally indicates the topic for the entire Web page and is where most people look first when they’re trying to figure out what the page is about. Since search engines first priority is to provide search results that people want, they try to use the same techniques to determine what a page is about. So content in the H1 tag will be considered most important and given a slightly higher rank than other content on the page.
If you’re trying to optimize a Web page for a specific keyword phrase, this is where that phrase should appear, preferably the first two words or so. This tells the search engine that these words are important – that this is what this page is about.
H1, H2, H3, etc. is a Table of Contents for Robots to Read
H1 Heading Tags Provide Structure and Pages Without Structure are Harder for the Robots to Read
When you structure your pages logically with one H1 tag, one or two H2 tags, and one or two H2 tags beneath the H2 tags, you create a page that is structured and easy to follow. Search engine robots are a little more simplistic than most people, but they are trying to index pages with the keywords that the pages are about. And pages that are structured to make it obvious what they are about (and the keyword phrases associated with them) will rank better than those that are not.
So the takeaway is that you should H1, H2, H3 tags to organize the topics that your article covers, in a hierarchical table of contents fashion. The broader the topic, the lower the number of the tag (i.e. H1). The narrower the topic, the higher the number of the tag (i.e. H6). Note that usually the lower numbered H tags are treated with more significance than higher numbered H tags in terms of how the robots try to figure out what the article is about- and how it ranks the article on the Google Search Engine for which which specific keyword searches.
For levels beneath the H1 title tag, you will have to use H2 and following tags. H2 header elements are used the most among the other five header tags. Follow with H2, H3 header tags after you are done with H1 for titles. Do not skip tags, as your document will lose structure and clutter.
If you use an important keyword in your H3, H4 header instead of your H2, search engine bots will give it lesser importance. H2 header tags can be used for subtitles with detail information, whereas the H3 or H4 levels can be used for lists with bullet pointing.
For SEO header tags other than H1 and H2 heading tags, search engines do not signify them. They can be used for deeply research content wherein content compartmentalization is necessary.