How to utilize those Market QR codes?
I have installed the application "Barcode Scanner" from here https://market.android.com/details?id=com.google.zxing.client.android 

To install an application, I open the "Barcode Scanner" application and hold the phone up to the barcode. It scans and decodes it automatically and then gives me the option to "open brower". I click on that and it eventually leads me to the Android market when I am given the option to install the application.