Basically they're these small square barcode looking things that contain info in them. What you do is use your phone's camera to take a pic of the qr code, then it'll show you the web page, or email or any other text that is in that code.
Here are two I made that have links for ordering Broken Chain on lulu.com, the other has a link to my website.
I made two using this QR Code generator. I'm using this app called QuickMark. If you have a symbian or Windows Mobile phone you should install it and try it out.
I'll probably add the website one to the back of my books from now on for my QR people who are in-the-know...