"When people talk about "what the law says" or "what the law is," they are generally referring to statutes (sometimes called codes). Statutes, which are created by the U.S. Congress and by our state legislators, attempt to lay out the ground rules of "the law."
(Nolo Legal Glossary, The Role of Statutes in Our Legal System, http://www.nolo.com/statute/).
"When most people talk about "the law," they tend to think only of statutes. But when disputes arise over the meaning of statutes, judges must interpret the statutes. Judges' interpretations of those statutes -- called "opinions," "decisions," or "cases" -- are as important to understanding what the law is as the words of the statutes itself. So once you find a statute that seems to address your situation, you might need to take the next step and see what the courts have had to say about it."
(Nolo Legal Glossary, The Role of Court Cases in Understanding Statutues, http://www.nolo.com/statute/).