A PIN Code (Personal Identification Number) is a secret personal code of 4 digits that you can use to block your phone. By doing this, you prevent other people from making calls on your phone.
When you buy a CHIPPIE SIM-card, the PIN Code in the phone is 0000. It's recommended to change this PIN Code as soon as you start using a SIM-card.
When a phone is blocked with a PIN Code, you must use that PIN Code each time you turn on your phone. If you use a wrong PIN Code several times in a row, your phone will be blocked. In this case you must use your PUK Code to unblock your phone.