Administrative Office of the US Courts: "Understanding the Federal Courts"
Read this report on the history, development, and organization of the US federal court system. Compared to the legislative and executive branches, the judicial branch did not receive as much attention in the drafting of the Constitution. The Constitution requires a Supreme Court, which the framers felt was a necessity if the national government were to have the power to make and enforce laws that would take precedence over state laws. As you may recall, the lack of a national court was one of the many shortcomings of the Articles of Confederation. However, the framers left it to Congress to create lower courts (also known as "Article III courts").
Click understanding-federal-courts.pdf link to view the file.