For a traffic citation/ticket:

You may pay your traffic fine in full, sign up for traffic school, or make payments on a traffic case already set up with a payment arrangement.

You may enter either your citation number, which is the entire number on the traffic citation/ticket, provided to you by law enforcement, or your case number which is the number on your bail quote and/or courtesy notice. 

For a criminal fine:

You may make payments on your criminal fine, if you have already pled guilty and have set up a payment arrangement.

You will enter your criminal case number.