There are two types of probations: Informal (court supervised) and Formal (Probation Department supervised).
For almost every single misdemeanor offense, when a person is convicted either by a jury or by a negotiated guilty plea, the standard probationary period is approximately 3 years. If the probationer for any reason does not follow through with their community service, payment of their fines, or enrollment of required classes (DUI classes, anger management, parenting classes, etc.), the court will issue a formal hearing to determine whether or not the probationer's conduct was excusable or not. If the failure to do some kind of term under probation was not warranted, the court holds the discretion to either add additional fines, jail time, or community service as a punishment for the behavior.
For most felonies and special misdemeanors, a person is placed on formal probation and is assigned a formal probation officer through the county department to keep a close eye on the offender. As with informal probation, the person may have tasks and assignments that must be fulfilled as terms to successfully complete the probation period..
If any of those terms are not satisfied, the probation department will petition the court to issue a violation of probation order that will ask for either an increased punishment to the terms of probation or a hearing to determine whether or not the probationer's conduct was excusable or not.