Headers aren't just for boosting readability, they also automatically generate an outline of the content contained within a document.
Table of contents tab
You can see your doc's outline via the "Show table of contents" button (indicated by the 4 line icon in the top right of your Slite app.)
Any text to which you've applied the H1, H2, or H3 headers will be listed (and linked toward) in the table of contents for your doc.
Table of contents embedded in your docs
You may also type /toc within a doc to place a table of contents in the doc's content.
Once you have your headers in place, you can bring order to even your longest docs. 📖