I was arrested on a Complaint and not an Indictment. How is that different?

This means neither a grand jury nor a judge have determined there is probable cause to believe you committed the crime charged. Instead, a statement accusing you of a crime is filed by the prosecutor. This statement (or Complaint) will have an attached Affidavit, signed by a law enforcement officer, describing the crime and the role they believe you played in it. You have the right to a Preliminary Hearing in front of the magistrate judge within ten days of your initial appearance if you are in custody or within twenty days if you are released from custody. At that hearing, the judge will determine whether there is sufficient probable cause to believe you committed the crime alleged and should be subject to further proceedings. Sometimes, the grand jury will return an Indictment before your Preliminary Hearing. If that happens your Preliminary Hearing will be stricken, or canceled.