From your smartphone or tablet you'll need to enable a setting that allows for the installation of apps from other sources. Selecting this option will allow you to install apps outside of the Google Play store. Take a look at the picture to see where this setting is located in different versions of the Android operating system.
If you have not already downloaded the app, then scan the QR code.
If you don't have a QR code scanner then get one! I would suggest searching the Google Play store for "QR Droid".
Now that you've scanned the QR code to download the app it's time to install. Head to your downloads folder and install the app.