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 station or on the back lock on the bicycle.
When you scan the code, you will hear the unlocking sound of the pin that holds the bike inside the station. When the pin is opened, you have to pull the bike out.
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.