Header or H1, H2, H3 etc. tags work like the headlines of a newspaper., They stand out from the text and your eyes gravitate toward them, scanning quickly to see what the next bit of content on your web page is going to be about. Following some simple but important rules will help your website get found faster and more often. This is one tip of many to maximize your ranking on search engines

You know what the title of your page is and you should also know what the content within will be about so using your keyword phrases as a focus in the page headlines should be straightforward and easy to do.Google and other search engines rank your headline tags in descending order. The H1 tag is the most important and ideally it should contain all the words of your keyword phrase. The H2 and other tags should be used as headlines for specific sub topics and is best if they contain only one or some of the words in your keyword phrase.

The H1 tag or the main headline should only be used once on any page. It should be used on every page and it's content should be keyword phrase rich, but different from your meta title tag. Your Headlines and titles should be different on every page. Search engines look for uniqueness and tend to avoid exact repeated content like you wold avoid spam. You can safely use as many H2, H3 tags as you like after. It is also a good idea to keep the HX tag hierarchy in order. H3 tags should come after an H2 tag but not after an H1 headline tag. Order them like you would your content.
H1-Main idea or topic
H2-Sub topic of the main idea - a branch of thought of the main idea
H3-Sub topic of the sub topic- a branch of thought of the sub topic idea
H2-Another sub topic of the main idea - another branch of thought of the main idea
H3-Another sub topic of the other sub topic- a branch of thought of the other sub topic idea
...etc