It's simply to share your app with a QR code. Here is how you do it:
Go to the yapp dashboard after you have logged in:
Click the Share button (Note: Your app needs to be published first before that button is available)
Click the QR code tab
Right click the large QR code and select "save picture as..."
🎉 Now you can use that image in any of your marketing materials! 🎉
To see more about your unique download link, see "How do I share my Yapp?"