The headings are used for splitting up the content file. An H1, H2 or H3 heading will dynamically split the document into new pages in the table of contents. An H4 heading is used as a heading within a page.
It is important that you insert any headings for new pages at the very end of the page you are editing, as all content below the H1, H2 or H3 heading will go onto that new page.