Common Law
Since law is an already complex field of study and even more complex wen put into practice, it is helpful to define and seperate the individual nature and quality of varying degrees of law within the government to better understand the law itself and its uses within society, especially with regard to common law and federal law. The basic principles of law in the U.S were established after the release of the Constitution. Since that time, law has developed and grown over the years based on those first principles, in regard to both common law and federal law. Among the varying degrees, areas and issues associated with law itself here is a simple break-down to help understand and interpret the major differences between common law and federal law. Being able to decipher bewteen common law and federal law will enable you to understand the basis for other aspects of law. 
Common Law- Common Law, for those who are not aware, is the type of law that deals with case trials brought before a court judge. These cases are brought to trial and are judged utilizing those precedents that were established by previous cases. Common law, originally invented in England is used to help build those precendents with each new tort or wrongful act that is committed by an individual. Within the United States, every state is required and responsible to conduct common law and determine case based decisions of torts brought to each individual state court. Common Law is also known as case law because of this fact. Property and contracts are two of the main principles and issues determined by common law within each state in the U.S.
Federal Law- Federal law holds its roots in the constitution developed long ago. In contrast to common law, federal law is governed by Congress and the government rather then the states. Federal law is determined by the legislation that is passed and the constitutional boundaries that limit it. Federal law can be passed after the President signs a bill into law. Federal law engulfs the areas and issues associated with, but not limited to, tarriffs, intellectual property, the military, money, anti-trust laws, railroads and avaition, pharmaceuticals and foreign affairs. Unlike common law Federal law is limited to the Constitutional statutes it must follow. Common law and common law courts have more case power in regard to the topics that are tried, simply because they are not bound by those statutes and are more decided upon based on precendents that are established on a case by case basis in varying states. Federal law is determined by the soverign power of the federal government and based on the principles established by the legislation that is selected and passed by that government. The people have more of a say in regards to federal law because we are able to vote on laws before they are passed into legislation. Federal law is in place for the safety of society as a whole and the individuals within it.