How do you go by getting a pin number to use card at ATM machines?
You should have chosen a pin number when signing up for your bank account. If you forgot it, go into your bank and explain the situation. They will verify your identity and get you a new one :)
Walk into the bank branch, and they can help you with that.
At your bank. You will need to show ID and do this in person.
They will send it in a separate envelope from the card. It depends on the institution as to whether you can change it