What are H1, H2,H3, H4 tags and where do I need to put them for SEO?

[quantumleap]

While related to Header tags you can go only up to <h6></h6>
it means there are only 6 tags

<h1>This is the H1 tag.</h1>
<h2>This is the H2 tag.</h2>
<h3>This is the H3 tag.</h3>
<h4>This is the H4 tag.</h4>
<h5>This is the H5 tag.</h5>
<h6>This is the H6 tag.</h6>