When you activated your Smartcard with QES at one of the Signature Sessions, you were asked to enter two different codes - your PIN (Personal Identification Number) and your PUK (Personal Unlocking Key).
You need your PIN every time you want to digitally sign a document, very much in the same way you need your card PIN when you use your bank card. Your PUK on the other hand is used when you want to unlock or change your PIN.
Very much like your bank card, you have three "tries" to enter your PIN. If you enter an incorrect PIN three times in a row, your Smartcard will be locked. Unlike your bank card, however, your personal codes are only stored on the Smartcard. They are in no database, they cannot be retrieved, they cannot be reset. They can only be changed by you.
We have put together a guide on how to change or unlock your PIN in case it becomes necessary; you can find the instructions here.
Please be aware that in order to be able to manipulate your personal codes, the card reader and the card manager software need to be installed on your computer. Without them, you will not have access to the codes and will not be able to change or unlock them either.