Probation in general:
If a crime is eligible for probation, and the judge grants probation as part of the sentence, then whatever the maximum time for the crime is gets suspended and a grant of probation is ordered. From there, the person would be told of certain conditions of probation – which may include county jail time up to a year. One of the standard clauses is that the person not violate the law.
If a person while on probation was to break the law (something of a felony or misdemeanor level, not just a traffic infraction), then the judge could find them in violation and impose any or all of the previously suspended time.
If the person successfully completed the probationary period without any violations and probation either expired or was terminated, then any suspended time is no longer an issue and cannot be imposed. Essentially, it’s a hammer hanging over your head to get you to comply with the law while on probation or face the consequences of not only your new charge, but the probation violation as well.