A subpoena is a court order that requires a person to appear in court to give testimony or to present documents and related articles to be produced as evidence at a hearing. A process server or officer will serve a witness personally with a subpoena. The City Attorney may also ask a witness to appear voluntarily without serving a subpoena.
If you have received a subpoena, follow the instructions on it. Failing to follow a subpoena is considered contempt of court and a warrant may be issued for your arrest.