Going trough the Federal Court
If you lose a case in a district court you can appeal to the US court of appeals which review the decision made in the lower courts. There are 12 appeals courts which cover their certain area in the US called a circuit. The thirteenth appeals court covers the whole US. The appeals courts cannot determine weather a person is guilty or innocent, instead they decide weather the first trial was fair.
Each court has their number of Federal Judges. The District Courts have 2, the appeal courts have 6-27, and the Supreme Court has 9 justices. The Presidents appoint all federal judges with the senates approval. If the senates decides they don't want somebody, the presidents just pick another candidate and wait for approval from the senate. The Judges job is to determine weather a person is guilty or innocent of a crime and who in a civil case gets their way. An attorney is appointed to help defend their clients case in a court. The US marshals are hired to protect everything that goes on in the court room.