A QR code is a 2-dimensional bar code. Barcodes are commonly found in the packages of products you buy and often hold a unique number. This unique number is often used to refer to a product. There are many online databases which allow you to then lookup this number and match it with the product.
You can use the QR code generator at http://qrcode.kaywa.com/ to generate QR code to your link, phone number or some text. To verify, you can use the Barcode scanner app or Google goggles on your Android phone :) (Hint : those are available when you search for them in the Android Market).