Often occurring shortly after an arraignment, a preliminary hearing can almost be classified as a trial before a trial. During this hearing, the judge determines if there is adequate evidence to bring the defendant to trial.
Before making a decision regarding probable cause, the judge listens to the stories from both sides first. The prosecutor may request that witnesses (if any) take the stand to testify, and can bring new physical evidence to the table in an attempt to persuade the judge that the case should go to trial. The defense often cross-examines the government's witnesses and questions any new evidence presented against the defendant, seeking to prove to the judge that the prosecutor's case should not go to trial because it is not strong enough.