Before reading any of the guides, you'll first need to have some prerequisite knowledge. First, you'll need to know HTML and CSS. Codeacademy is a great place to learn HTML and CSS (and other languages) for free. Then, you'll need to know some terminology. The Book Designer's Joel Friedlander has a list of publishing terminology related to books and ebooks that you'll need to know and lastly, if you want to see the inside of an actual ebook to use as an example, I suggest using Calibre to open up ebooks you own and see inside.