It is a hearing in the District Court with sworn testimony where the judge, the defendant's attorney, the prosecutor from the District Attorney's Office and any victim or witness subpoenaed are present. The purpose of the hearing is to establish a) that a crime has been committed and b) that the defendant committed it.
The burden of proof lies with the prosecutor to show probable cause. Usually, the defendant offers no defense. If the judge finds probable cause, the case is sent to Superior Court for presentation to the Grand Jury. The defendant may and often does waive the probable cause hearing. If the judge does not find probable cause, the court dismisses the case. The case may still be presented to the Grand Jury. The probable cause hearing is an intermediary step, but is not a finding of guilt or innocence. Probable cause hearings are open to the public.