After you’ve completed pricing and territories, click the "Files" tab in the upper left corner of the iTunes Producer screen. Then drag and drop your completed EPUB onto the left portion of the screen, under Book.

You’ll drag and drop another EPUB with only a few chapters under Sample, so that readers can take a look at a sample of your book before buying. You don’t need to do that unless there were particular pages you wanted to include in a sample. Apple will automatically produce a sample if you choose not to upload one.

Click "Submit" in the upper right corner of the iTunes Producer screen when you are ready to upload your ebook.

And that was! Your ebook should appear in the iTunes Store and iBooks Store within 72 hours or less.

To view your ebook in the iBooks Store, log into "iTunes Connect", click "My Books", select the ebook you wish to view, and on the right side of the iTunes Connect screen you’ll see a "View Book" link. Click the link and it will take you right to your published ebook sales page.