A QR code is a type of barcode that is quickly scannable by the camera in most smartphones. Inside the code is a URL that your phone opens in the browser.
To scan the QR code, open your camera app. If you're using an iPhone, when the camera has focussed on the code you'll see a notification prompting you to open Safari. If using an Android, point the camera at the QR code and tap the code on the screen, after this, you will see a popup at the bottom of the screen prompting you to open your browser.