The purpose of legal research is to find "authority" that will aid in finding a solution to a legal problem. Primary authorities are the rules of law that are binding upon the courts, government, and individuals. Examples are statutes, regulations, court orders, and court decisions. They are generated by legislatures, courts, and administrative agencies. Secondary authorities are commentaries on the law that do not have binding effect but aid in explaining what the law is or should be. The resources available to find legal authority are vast and complicated leading many law schools to require students to take a class in legal research.
http://www.law.cornell.edu/wex/legal_research
http://www.law.cornell.edu/wex/legal_research