First off - Welcome to MR!
This post should probably go in the Sigil forum since it is asking about Sigil issues. Also, if you could provide a sample of the coding/error it may be easier to figure out what's wrong.
In the meantime here is some basic advice:
1) use Sigil's auto ToC generator (in the Tools menu). Sigil does a great job with all the nit-noid background requirements in creating all those pages and putting them together into an ePub properly.
2) Page Edit is a basic WYSIWYG editor that is best used to correct typos and other minor mistakes rather than creating the book files in the first place. I would recommend using a good word processor that has all kinds of built-in features to make an author's life easier. There are a few free ones that do a great job like LibreOffice, GoogleDocs, etc.
Create your books there then save them as HTML. Then it is really easy to 'Add existing' files to Sigil and let Sigil do all the background magic.
There have been a few discussions here about best practices when using these word processors. Some even have links to tutorial vids. Just search the threads, you should quickly find ones from
Tex2002ans. The biggest thing to do is to get comfortable with using styles, and then
consistently use styles!! Set the chapter/title/part headers AS headers <h1-6>...Sigil uses those headers to automagically create/maintain your ToC.