I'm not sure you want to use Sigil yet. Or at least, if you do, you need some basic HTML and CSS knowledge.
If you already know HTML and CSS, making an ePUB book is not hard, you can have a look at
this tutorial for a first contact. A Mobipocket book is maybe easier, but less flexible, it's basically a stripped down HTML (see
here), but you would need some tool to convert it to mobipocket (I use MobiPerl's html2mobi).
I'd be glad to provide source files of my mobis, and to give further advice if you have more specific questions.