Gosh epublishing is complicated.
If you want to sell on Amazon, you convert your book into .MOBI, and upload it with information like the blurb, the ISBN (not essential), the author etc.
Barnes and Nobel want a different format, but the procedure is similar. As with Kobo.
But Apple, Sony, Diesel and (I think) Aldikon won't deal with small publishers like me. You have to go through Smashwords.
Who are Smashwords? Well, you send them a very, very carefully formatted .doc file, and they create the other formats, submit them for you, and centralise the sales data and royalties. Oh, and they throw in a free ISBN. For which they take 15% (on top of what Apple or whoever take). Lots of people find that a good deal, but a) I don't need their formatting, b) I currently have the book as a .pdf, so it would need redoing, and c) I don't have MS Word, just Open Office. Now Open Office is almost the same, but I gather that the tiny differences are enough to really sugar up the conversion to other formats.
I gather Smashwords is fine for a lot of writers, but not for me.