moLOCAL love using QRDroid for the Android Phone system. We have found this, by far, the best scanner for android and with 5,000,000 downloads it's hard to argue.
If you are using a smartphone with another operating system we have compiled a collection of the best QR readers for a wide range of smartphones here
Go to your appstore, download and install your reader software. QRDroid is a relativly small install and should not take too long to download on a normal 3g network connection. 
Instructions are easy and self-explaintory. Choose Scan from Camera, you should get a screen similar to that on the right >>.
Best practice for easy and fast results is to hold your camera as parallel to the code image as you can.
The software will automatically try to 'lock on' to the code's 3 position tags in the corners and (if present) the alignment tag. You may notice, depending of the software you are using, a series of blue dots dart around the screen. This is the software working.
QR Codes are designed to read/decode at very high speeds so this process should not take very long at all. Please bear in mind that smaller codes, those with a lot of information to recover and some badly customised codes may take longer to scan.
With your code successfully scanned the information it stores should automatically show in its desired format.
For a webpage, for example, just select Go to URL to open the web link in your desired browser.
Don't forget to add to favourites and bookmark any websites you are planning to revisit in the future.
Code Results can produce a wide range of results including:
GeoLocation, Telephone Number,SMS Link, vCard Details, Address, Email Address - all with their own specific options.