Here are quick google links I've used to help out many (non-comic book) clients. And when I mean help out... I literally said to everyone of them... "save your money and do a little reading."
AND the DROPDEAD simple way to go... if you are on a Mac or iPad... http://support.apple.com/kb/HT4168
Basically an ePub is a ZIP document that has images placed into simple mulitple letter sized html documents with hyperlinks. ONCE you zip compress the directory, change the ".ZIP" extension to ".ePub" it then becomes an ePub document which can be read on any device that reads the ePub format... which I think is all of them.
WAIT WHAT!!? HOLEY SMOKES! That's b0tsh$t insane. It can't be that easy!
Yes it can... but take your time, do a little reading and play a little with all the wonderful options available to you through the starter links.
Including this link: http://www.ommhub.com/using-the-apple-ibook-store-to-sell-your-books/