Headings are the titles of your page. Notion only provide h1, h2 and h3.
<h1 class="notion-heading1 notion-color-default">
Congestosque commeatus
</h1>
<h2 class="notion-heading2 notion-color-default">
Taliaque summo
</h1>
<h1 class="notion-heading3 notion-color-default">
Heading 3
</h1>