When you have successfully guided yourself to the closest bicycle, you can easily unlock it, by tapping the "scan QR code button".
A camera mode will open, and you should point your phone to the QR code on the handlebars or on the rear mudguard on the bicycle.
When you scan the code, you will hear the unlocking sound after a few seconds.
Congratulations! The bike is now rented and you can start biking... Oh, one more thing... before you start please make sure that the bike is in good condition.