Aiding and abetting are terms of usage in the criminal law which mean that another person helped the primary person do whatever criminal act for which they are charged. Aiding or abetting can vary from driving a car, to being present at a fight and rendering assistance or being a lookout for a burglary or robbery or any other crime.
If a person is convicted of aiding or abetting, they are convicted for the same level of crime in which they asisted as the person who actually pulled the trigger or did the burglary. However, often times a prosecutor will allow the driver, who could claim he/she didn't know what was to happen or claim they didn't know there was a gun in the car, a lesser deal in order to get them to turn on the primary mover who really did the crime. Its called a plea bargain because the person gets the benefit of a lesser crime to which he/she can plead guilty and he/she gives information about the other actor that will help to convict him/her more easily.