A summons or subpoena is a common tool used by lawyers to mandate that witnesses show up to hearings and/or provide information. If served with a summons, it is imperative that you abide by it or face contempt of court (which could include fines and/or possible jail time). Being subpoenaed to be a witness does not mean that you have done something wrong, just that a court is compelling you to appear and tell what you know.You can inform the police or the district attorney that you do not have much information to give them, but most law enforcement officials would probably want to interview you anyway to make sure. From what you described, it does not initially sound as if they want to charge you with a crime. However, that all can change depending on what you tell them once they do interview you. If the police call you into the station for an interview, ask them right away if you are free to leave. If they say yes, then know that you do not have to answer any questions that you feel uncomfortable asking and can leave anytime. If they say no, then they must read you your Miranda rights before asking you questions, or risk having your answers thrown out of evidence.In any event, it does not seem from the information you provided that you have much to worry about. However, I would always advise to seek an attorney to make sure you do not say anything that could possibly incriminate yourself or make you an accomplice. In general, consulting with a criminal defense attorney beforehand is preferable anytime you have to speak to the police or law enforcement and you have the possibility a criminal charge, no matter how frivolous or improbable being convicted may be. It is always better to be safe in these situations that risk incriminating yourself and face possible charges.