After one is convicted of a crime, there is usually a probation period wherein he/she is court-ordered to comply with certain conditions.
Examples of these include: serving jail time or doing some sort of work in the community, paying fines, making restitution, and following the recommendations of a chemical or psychological assessment.
The probation department monitors whether the individual has tended to these obligations.
If there’s a problem, he/she will be either notified by mail of another court date to address the probation violation, or, unfortunately, are simply arrested and brought to court directly from jail.
If any jail time or part of a fine was "stayed" at the original sentencing hearing, a probation revocation can result in serving that time and/or paying that fine after all.
In other words, though one may not have completely understood or appreciated it, their original sentence probably included jail time and/or fines "hanging over his/her head." If it is determined that there has been a probation violation, this jail time and/or fine may now be imposed after all.
One has the right to contest a probation revocation hearing.
An experienced attorney may be able to provide the probation officer and/or court with an excusable explanation, and/or an argument that one should be given one more chance to prove that they will abide by the original court order.