Headings Are Important
Heading tags are very important tag in HTML document; it helps to make the content organized and reader friendly, and the content inside heading tag tells search engine what are the important subject on that particular page, thus helps in SEO
Headings are defined with the <h1> to <h6> tags.
<h1> means the most important heading.
<h6> defines the least important heading
Here are some example how you can define Heading
Headings Font Size
Each HTML heading has a default font size. But you can specify the font size for any heading with the style attribute using the CSS font-size property, in your css file you can setup the default size for each heading.
Now when you define a heading in your webpage, it will take the default size you have set in your css