Re: Is there a guide in book form to learn about using the iPhone 6S?
Welcome to iMore. Here is a link to the Ultimate Guide on using an iPhone 6s/6s Plus. Or you can use this link for another guide created by Apple. You actually want to learn about IOS 9.2 which is the most current software running on the iPhone 6s/6s Plus. I realize they are not books, but they are really good guides and should assist you very nicely in learning the iPhone.
I watched iPhone 6s Complete Beginners Guide on YouTube when I first got my 6s, and it was soooooooo helpful!. I may go back and watch it again. The video is actually showing the 6s Plus, but it will still help you with the 6s.