Bakari Chavanu over at our sister site Apple Matters has an excellent review/tutorial on the Kindle app for the iPhone. From the article:

First off, if you have used a few other iPhone app ebook readers like Stanza or eReader, you’ll find Kindle for iPhone lacking by comparison. But the Kindle for iPhone basic interface won’t keep you from using the app. All your downloaded chapters and books can be browsed by Recent view, Title, or Author. You can also delete or archive books and chapters on the Home page. You can change the font size of books, but other than that there’s no other options for changing the application’s interface. 

Read Bakari’s entire post, filled with info, over at Apple Matters.