Answer Updated: Dec 03, 2018
QR codes are barcodes that contain information. They allow printed material to 'link' to a website when you scan the code with a smartphone.
Both iOS and Android now have built-in support for QR codes - your phone will automatically recognize the code and give you the link, when you scan the code with your camera app.
You can also download a QR code app from your app store if you wish.