Well in a nutshell, a 2d code is another way to encode information just like the more popular barcode. However, the 2d code is grid of square cells that are capable of storing more information and more character types all in a smaller space.
The 2d code has been very successful in Japan for a couple of years now and will continue to be due to its convenience. That’s right, I said convenience. 2d code is easily readable by your mobile camera phone with the help of some encoding software that transfers data to your web browser. Simply snap a picture of any 2d code (preferably the one on your left) and sit back and enjoy the ride.