Where do I find the 6 character code?

I find MIT App2 in Appstorem but it shows to enter 6 character code.
What does it mean?

From your project on http://ai2.appinventor.mit.edu or http://code.appinventor.mit.edu, select the AI2 Companion from the Connect menu. A QR code and the corresponding 6 character code will appear. Scan the QR code or type in the characters to connect up your device to the website and start testing.

At the moment you can only test your apps, the build functionality to package the project into an app is coming later this year.

I see!! Thank you very much.