At a preliminary hearing, the State must show that the charges are based on probable cause (a reasonable person would believe a crime was committed, and that the defendant committed the crime). The Court must find substantial evidence to support probable cause. Generally, there is just one witness and it is a police officer who testifies to the entire investigation.
A preliminary hearing can be waived, which is when a defendant can give up his or her right to the hearing. It is generally waived at the initial appearance.
If the judge decides probable cause has been established, the case proceeds.
If the judge decides probable cause has not been established, the Court dismisses the case without prejudice. This means the defendant is released and any paid bond is returned. This may occur if a witness fails to appear to testify. The prosecuting attorney may still re-file the case and continue to prosecute.