The PIN code provides protection for your mobile phone. If you forget your PIN code, then the security system prevents you from using the phone.
Try not to enter the wrong code more than twice: on the third wrong try your phone is blocked by the SIM. If you were mistaken and the phone is blocked, don’t worry. You can still contact your service provider’s customer service department and they will give you a PUK (Personal Unblocking Key) code to unblock your phone.
Note: There might be a fee for this service, depending on the service provider.