[jackie_w]

If you're most comfortable with MSWord as your creation tool then the simplest workflow is to

1. Open your .RTF or .DOC file in Word
2. Mark chapter headings/sub-headings with the built-in Word styles 'Heading 1', 'Heading 2', etc 'Heading 1' is equivalent to <h1> in html, 'Heading 2' to <h2> etc etc
3. Don't bother including chapter page breaks in the RTF/DOC, Calibre will insert them for you at chapter breaks.
4. File - SaveAs - Webpage-filtered. This will create an HTML file (plus a directory containing any embedded images if there are any)
5. Import the resultant HTML file into Calibre, which will also automatically include relevant images from the image directory. Calibre will change the HTML file to a .ZIP file during the import.
6. Use Calibre to convert ZIP-to-MOBI making sure that the Convert - StructureDetection page contains a suitable entry in 'Detect chapters at' box to match what you did in step 2. Set 'Chapter mark' to 'pagebreak'
7. Fill in the Level 1 TOC and Level 2 TOC boxes on the Convert - TOC page, again to match what you did in step 2.
   If your TOC only has one level, I think you can skip this step.