The US District Court
Most federal criminal cases are tried in US District Court.
Generally, federal criminal cases are tried in US District Court.
Federal trial courts almost always have original jurisdiction in the federal system.
Federal appellate cases
Most federal cases begin in the district courts.
Most cases reach the US Supreme Court via the US Court of Appeals Circuit Courts, which are part of the federal court system.
State courts, by far, hear more cases per year than all of the Federal Circuits combined.
Civil law
US District Courts have original (trial) jurisdiction over the majority of cases heard in the federal court system.US Special Courts, such as US Tax Court, US Bankruptcy Court, and the US Court of Federal Claims, also hear a large number of cases.
The Supreme Court of the United States was created in 1789. Most of the cases the court hears come from lower courts. Each year, the Supreme Court receives 7,000 or more requests to hear cases from lower courts.
In most cases I have read the civil cases heard at the Federal level are cases that directly question someone's rights and apply to a large number of people. The cases heard at a local level can also be promoted to Federal cases. For example if you have a property dispute with your neighbor it will not go to federal court; however, if you have a court that disputes whether its legal for you to carry a concealed weapon or practice free speech you could proceed to the Federal Court.
The U.S. District Courts since that court is the main trial court.