Although the U.S. Supreme Court is the highest court in the federal judiciary, Congress has established two levels of federal courts under the Supreme Court: the trial courts and the appellate courts.
The U.S. Court of Appeals for the Fourth Circuit is one of 12 regional circuits - each of which has a United States court of appeals. A court of appeals hears appeals from the district courts located within its circuit, as well as appeals from decisions of federal administrative agencies. The U.S. Court of Appeals for the Fourth Circuit hears cases from the district courts located in Virginia, West Virginia, Maryland, North Carolina, and South Carolina.
The United States district courts are the trial courts of the federal court system. Within limits set by Congress and the Constitution, the district courts have jurisdiction to hear nearly all categories of federal cases, including both civil and criminal matters. There are 94 federal judicial districts, including at least one district in each state, the District of Columbia and Puerto Rico.
The website for the federal judiciary has a lot of great resources, including a handy e-book entitled Understanding the Federal Courts and publications and reports. The Federal Judicial Center also has other great resources you may want to take a look at.