For this to work you must have installed iOS 6 on your i devices (iPad, iPad mini, iPhone). It might work with an iPod touch but I have no way to test it.
If you have iBooks and/or Kindle installed on more than one of your devices and you download books to read you will discover that Apple has built in a cool new feature in iOS 6.
Say you are reading a book on iBooks, but you left your iPad at home and find yourself sitting at the doctor’s office with nothing to do. You can now open your iPhone, find the book you are reading and it will open to the last page you were reading on your iPad.
I think that is just awesome.