Suzanne, as I mentioned before there are a lot of tutorials that will help give you a basic understanding of what an ebook is; gives references to good authoring software and even gives example ebooks from MobileRead's free library that you can study. These are included in
MobileReads wiki.
In that wiki you can also find a section that talks about the issues with creating ebooks:
eProduction.
I think you are trying to use a very powerful tool without knowing how it works and are getting frustrated. It takes a little bit to learn how to do this yourself. Look through the tutorials, read Sigil's User Guide, and you will have a much better idea of what's going on.
One BIG piece of advice...don't try and create a book for publication by yourself without knowing all the issues... Authoring software that can "save to ePub" format is only the first step. You need to understand the rest of the process - like what are all the different reading device/apps peculiarities, how to format your book so it passes the intake process of whatever publisher you are using (amazon, smashwords, apple, kobo, etc.), the best way to style your book to take advantage of those publisher's selling features (like amazon's Look Inside). If this is too much to do right now, then talk to a professional ebook designer. It is WELL worth the added expense to avoid the frustration and to make sure you present your brand (your name) in the best way possible. I would
PM Hitch...she's in the business and very respected in the community.
Cheers,