Both civil and criminal cases are tried in federal court. A civil case involves a dispute between two or more individuals or corporations. The party bringing the action may request monetary damages or may ask the court to order the defendant to perform or stop performing certain actions or both. In a civil case a person called the plaintiff files a complaint against another party, the defendant, who then must file an answer to the complaint.
Criminal cases are also tried in federal court if they involve breaking a federal law. In the federal court, a criminal case must be brought by the U.S. Attorney who serves as the attorney for the government. The evidence alleging the individual committed a federal crime must be presented to a grand jury and if the citizens on the grand jury agree, they issue an indictment. The person is then arrested and required to plead "guilty" or "not guilty" to the crime. If the person pleads "not guilty," he or she must have a trial.
Additional information on Jury Service in Federal Courts is available on the U.S. Courts website.