If we are talking about the password on the blackberry itself, to unlock the device, then it is a password that you, the user set. What I understand is you purchased a used (second hand) blackberry that was still password protected from the previous user.
If the above is the case, there's nothing you can do but enter the wrong password repeatedly until you max out the allowed number of attempts, and the device will wipe and reset. You will not be able to unlock the device unless you know the password.
Once it wipes and resets, you will be able to use it. You can set you own password, or use it without password protection.