Do not use headings for SEO. Use them to give structure to your page.
Every page should have an <h1> for the top heading. (Some people say pages should only have one <h1>, others say you can have more than one)
Any sub-headings should be marked as <h2>.
Any sub-sub-headings should be marked as <h3>.
And so on down the line until you get to <h6>.
In practical terms, most pages will only need to go down to <h3> at most.