Litigation is the process of going to court to argue your case. The case could be criminal, in which the state argues that a citizen violated the law, or civil, in which two citizens or businesses argue against each other. Within each of these categories, there are several other smaller courts. For example, criminal cases about traffic violations or youthful offenders have their own courts, and civil cases relating to housing, family, and bankruptcy often have their own courts.
Some litigation also takes place in administrative courts, such as the IRS's tax court or the Executive Office of Immigration Review's immigration court. Although exact procedures vary by court and by state, most trials follow a similar pattern. One side, known as the "plaintiff," "complainant," or "prosecution," files a complaint listing out all of the ways the other party broke the law. The other party responds by admitting or denying the items in the complaint.
Then there is an investigative period known as discovery, in which both parties investigate the facts of the case. The parties will attempt to resolve their issues many times over these initial stages, but if these attempts are unsuccessful, the case will go to trial. A judge will preside over the trial to ensure that the law is interpreted accurately and that each side follows procedure. Sometimes the judge will also decide the facts of the case, but sometimes that task is left to a jury.
If either party believes that the judge made an error in her interpretation of the law or procedure, that party can appeal the case to an appellate court, which will then review the judge's decisions for accuracy. When the appellate court judges find an error, they will often send the case back to the trial court for correction.