A subpoena is a document which summons an individual to court on a specified date and at a specified court. The subpoena may also include the requirement that the individual bring certain documents or other items when they appear in court.
Those that have been subpoenaed must appear as specified. Individuals should arrive early and expect to wait until they are called. If there is some legitimate reason why the individual may not be able to appear as specified, such as a scheduled surgery, they must immediately notify the courts or they could face charges for contempt of court when they fail to arrive.
Individuals that choose to ignore a subpoena, can face serious consequences, including jail time. When individuals do not appear, the judge will likely issue a warrant for their arrest.