Any idea you have that the ebook file is like the print book file, forget it. It's not the same as the original file either, though it is similar. The ereader used to read the book will format the pages depending on the font and page size selected, so you have no control over that. You can force a new page for a new chapter, but that's about all.
The front matter is different too. All you need is the title, your name, publisher, copyright, and a paragraph about the ebook edition licence which Amazon or Smashwords will give you. I put the ISBN in too. And they go one after the other with just a blank line in between, nothing fancy. Then you have the Table of Contents (TOC), if you're using one, and then the book starts.
The TOC can be set up using bookmarks and hyperlinks so that the reader can click on a chapter in the TOC and go straight there, and click on a chapter heading and go straight back to the TOC. It's a bit fiddly, but not hard to do, once you know how to create a bookmark and a hyperlink.
Don't use fancy fonts and formatting unless you're really sure what you're doing, it's best to keep it simple. Especially don't use tabs for paragraph first line indents (use a paragraph style in your word processor), or lots of blank lines. Also, in a print book you should hyphenate long words if the word wrap leaves a big space at the end of a line and justify the text (straight right hand edge). For an ebook you don't know where the end of lines are going to be, so no hyphens and don't justify.
Separate each chapter with a blank line and four asterisks, like this:
At the end of the book, put three hashes, like this:
There are things you should put at the end of the book, like your short bio and contact details (remember that hyperlinks work in an ebook, so they can click and go straight to your website or other page, if their reader can handle it). If you have other books you could put an advert for them and a link, or even a sample chapter. You might also want to include a polite request for a review, although Kindle automatically asks for a review when they reach the last page - but in case they don't page through your extra stuff at the end, you might want to put in your own request immediately after the end of the book.
For detailed advice read the Smashwords Style Guide (which you can download and keep) and the similar advice on Amazon for Kindle. Double- and treble-check your manuscript for spelling and grammar errors before you submit it, and always check the converted version thoroughly. Smashwords includes an automated checker that will pick up some conversion errors, so even if you're not using Smashwords, it's worth submitting the book and getting it checked and then taking it down again.
If this sounds like a lot of work, it's really not, especially compared to formatting for print. Kindle is slightly different to Smashwords (which converts to all the other formats) so you will need two ebook files, one for each, if only to change the licence notice.
One last thing: they told me you can't get pictures into an ebook, or at least it's extremely difficult. My book, Alina, The White Lady of Oystermouth, has a beautiful line drawing at the beginning of most chapters. I put the pictures in my ebook files and submitted them to see what would happen, and they converted with no trouble at all. So if you have pictures, give it a try.