A QR code (short for Quick Response) is a two-dimensional code originally designed in Japan and initially used in the auto industry. You can use them to encode and store textual information, link to a web site, a vCard, etc. For more information refer to Wikipedia
In order to be able to read QR codes with your smart phone you need to install a QR code reader. Here are some suggestions:
Android – i-nigma Barcode Scanner
Windows Phone 7 – NeoReader
BlackBerry – ScanLife Barcode
There are many QR readers out there – it is up to you to choose the one you like the best.
So what about generating your own QR codes? You can do this as well. Go to http://goqr.me and start creating your own QR codes for free.
Here is some video on you tube about how to use QR code with vCard: