If you want to read a bit of the QR history, go to Wikipedia
Locally, they are being used to provide 'Coming Attraction' lists for movie houses, links to Google Maps to show how to get to particular places, and price lists for retail outlets.
The usual mode of use is to install an app on a smart device, scan the QR code, and let the app do the work.
Some useful apps are:
iPhone : Neoreader, i-nigma, Optiscan, Barcode, QuickMark, Scanlife, TapMedia, QR Pro, QR Scanner
Android : Barcode Scanner, ShopSavvy, Scanlife, QuickMark, QR Pal, i-nigma
Blackberry : Scanlife, Bee Tagg, QR Code Scanner, i-nigma
Windows Phone 7 : PhraseMeme, QR Reader, Stripes, Bee Tagg, NeoReader, QuickMark, i-nigma