You can start by entering your phone number, then you will receive a 6-digit code via SMS to enter into the app. If you can immediately access the app after that, everything is fine. However, if the app asks you for a 12-character housing code, you'll probably find this in your SMS, email or on a piece of paper, and then you can type it into the app. If you can't find the apartment code, you can ask your landlord or landlady for it.