Here is a cute Common Craft video that explains QR codes and what they can be used for..
QR Codes by Common Craft videos
QR codes are more familiar to students than teachers. I've used them to post summer reading lists, direct students to LibGuides over certain projects or showcase orientation information for new students. You could write book reviews, post them to your online catalogue and then add a QR code to the spine of the book to help students know more about a title.
What other uses for QR codes can you suggest?