If you want to learn more about QR Codes check out the explanation from Common Craft.com
Below is a collection of links that were shared from Listly.com I think you will find some great resources to get you started with QR Codes.
In addition to the links above qrphoria.com offers some really interesting ways to customize your QR Codes. Make sure to check them out as well.
Customize your Twitter page with these options from around the web.