The "Outline" section in Frase's right side panel is meant to be an ideation point for your header structure by gathering headers across the top Google results.
Open the "Outline" tab and click "Explore Headings" to see the search results view.
Then scroll horizontally to view the different header structures, and simply click headers to add them to your right side view.
Tap the header tag in your right-side view to bring up a dropdown of H tags (if the goal is to change the H tag of a header). Click the 3-dot icon on to the right of the header text for options such as editing the header, or adding a new header above or below the current header.
See header settings options below.
When finished gathering/editing your heading structure, tap the "AI Article" button to use the AI Article Wizard to write the full article. Or just click the paste button to paste the headers into your editor.