To use the QR Code Scanner, have the Ticket Holder present their Ticket Confirmation to you, either by displaying a copy printed on paper, or by their mobile phone screen. Click "Scan", and use your mobile phone camera to scan the QR Code.
QR Codes are square-shaped "bar codes". They contain encrypted information that the Muscleware Ticket Staff Web App can read, and automatically find the ticket purchase/transaction for you, saving you from having to search by Name or Receipt Number.
Below is an example of what a QR Code looks like: