If text within a section is not showing up in the preview
Check to make sure you are not typing within one of the Section Headings or Subsection Headings.
If a section's title is not showing up in the preview
Make sure that there is text within the section. Sections with no text might not appear in the completed file.
Please see the image below for examples of a Section Heading, Subsection Heading, and the text within a section.