Amazon owns a fairly large share of the eBook market in the United States, but they are not the only retailer and they don't sell books in every country.
There are actually dozens of different eBook retailers, such as iTunes, Kobo, Nook, Torino, Smashwords, Playster, Scribd, OverDrive, and Google Play (just to name a few.)
One thing that almost all of them have in common is that the file format they sell is ePub, which is an open source eBook file format. Amazon sells files in their own proprietary formats, Mobi7 and KF8. (One little known secret is that you can upload your ePub files to Amazon and they'll automatically be converted into Amazon's formats!)
In this training, Blaine walks through how to use a free tool called Sigil, which lets you edit your ePub files directly without having to know how to unpack and repackage them back up.