Headings run from <h1> to <h6>. <h1> should be the page's main title, and using it just once per page is generally better for SEO and readability.
Headings aren't for making text look bigger — they're for showing content hierarchy. Making the font pretty is CSS's job, so don't ask HTML to moonlight as a stylist.
html
<h1>HTML Full Tutorial</h1>
<h2>HTML Basics</h2>
<h3>Elements and Tags</h3>You should see
You should see three levels of headings, reflecting the content hierarchy.