QR codes are the next generation of "bar" codes. With the proper scanner on a smartphone, the QR code helps people to reach websites.

Go to the app store for your particular smartphone to find a "bar code" or "qr code" scanner. You can find free apps for that. Install the app on your phone.

The app uses the phone's camera. Open the app and point the camera at the qr code. The phone will respond once it has picked up the information (you might have to experiment with how close or far away from the code your camera needs to be). Once you have gotten to the website, you can bookmark it or use whatever other features your phone has for websites. For example, you might be able to send the url to your email so you can access the website from other devices.

It is easy to generate qr codes. Here is a generator that yields a .png file that can be added to documents:
http://www.qrstuff.com/

You can also create business cards with a qr code. One way is to upload the .png file in place of a logo on this card:
http://www.degraeve.com/business-cards/

Here is another place:
http://businesscards.tec-it.com/

These sites yield .pdf files which can be printed and cut apart.