For the purpose of legal research the term "cases" or "case law" refers to opinions written by judges, usually on the appellate level, which resolve litigated disputes. In deciding cases, appellate judges base their reasoning on statutes or previously decided cases.
There are several points to keep in mind when conducting case research:
Opinions of the highest level appellate court of the jurisdiction are the most important mandatory authority. If the highest level court has ruled on a matter, that ruling binds any intermediate level appellate or trial courts in the jurisdiction. If the highest court has not ruled, the rulings of intermediate level courts are the best authority which can be found, but they do not bind the higher level court in any subsequent proceeding.
When researching, it is usually most efficient to seek out and read the most recent cases first and work your way back. The most recent cases will: a) reflect the current state of the law and b) contain citations to, and discussions of, earlier relevant cases.
Remember that the one-paragraph summary of a case (known as the syllabus) and the headnotes which precede the court's opinion are provided by the editors of the reporter, and do not constitute part of the actual opinion, although they often quote or paraphrase its actual text. Headnotes and syllabi are useful research tools because skimming them may allow the researcher to eliminate irrelevant cases. In order to fully understand the holding of a case, however, you must read the opinion in its entirety.
Keep in mind the distinction between holding and dicta. The holding is the part of the opinion which is central to deciding the issue before the court; it is characterized as the law applied to the facts at hand. Dicta, on the other hand, refers to parts of the judge's opinion which are not essential to the resolution of the dispute before the court. Language in an opinion which can be characterized as dicta is not binding on subsequent courts.