Here you will find an explanation of the information contained in your PIN letter:

Whenever you want to use the eID function, you will need your personal six-digit PIN. You must set this yourself. You do this by replacing the five-digit activation PIN (also known as transport PIN) from the PIN letter you received from your authority with your personal six-digit PIN. You can do this either on your computer at home using a card reader, or with an NFC-enabled smartphone or tablet. Alternatively, you can do this on site at a citizen terminal in public authorities.  

You need your PUK to reactivate your eID function if you entered your PIN incorrectly three times. To reactivate it, you must enter the PUK. The PUK can be found in the PIN letter that you received after you received your electronic ID card.

Your CAN is located on the front of your ID card - on the top right of your German ID card and eID Card, and on the bottom right of your electronic residence title. You must enter it, for example, if you have entered your personal six-digit PIN incorrectly twice.

You need the blocking code if you have lost or stolen your eID. In this case, you should have the eID function blocked by the authorities or the blocking hotline as soon as possible. To do this, give them the blocking password from the PIN letter you received.