Headings should be assigned incrementally based on the heading's importance. The title of your page (in the title field) automatically is assigned H1. There should be only one H1 on a page. Each subsequent heading should be assigned based on whether it is a sub-heading to the title (H2), a sub-heading to a sub-heading (H3), etc.
To assign a heading:
- Highlight the text you wish to use
- Click on the dropdown marked 'Paragraph'
- Select the heading level appropriate for your text