Hi templario,
I'm using Smashwords, a distributer for ebooks. You upload your book to Smashwords, and they send it to stores like iBookstore, Sony store, etc. When you sell copies, they take a share of your profits. As far as I know, you need to use Smashwords (or similar services) to get your book into these ebook stores.
An exception is the Kindle store; you can use Amazon's Digital Text Platform to do that yourself. I uploaded my fantasy novel "Firefly Island" to the Kindle store myself last week. It was easy to do, and I'm able to log in anytime to view my current sales.
Daniel
http://www.DanielArenson.com