The Book Creator app for the iPad is with limitations in terms of capabilities but you can make an ebook with it that you can publish on to the iBook Store. The best way for beginners is to go via an aggregator like Lulu or Smashwords. when you get more adept at the eBook publishing then you can buy your own ISBN numbers and deal direct with Apple.
The other advantage of using Lulu would be that you can get your book into the Kindle store too.
