The badge scan is a feature available only from the mobile application. It is materialized by a camera-shaped button at the bottom right of the screen, on the home page.
To scan a badge, simply approach the QR barcode or normal barcode with your camera. This way you automatically add the person to your contacts (and you're added to theirs). This allows you to exchange messages, obtain contact details, rate the quality of the contact and add notes about them. Your contact details are also automatically sent to him/her.