When lawyers and law professors refer to "cases," they typically mean the written opinions of appellate court judges. Opinions from appellate courts can be crucial to understanding a given legal issue because such opinions affect how lower courts decide similar issues in the future.
Citation: A reference that identifies a particular case, law review article, book, statute or other resource. For example, the citation for Roe v. Wade is 410 U.S. 959 (1973). The case appears in volume 410 of the official United States Reports (United States Reports is the official reporter for all US Supreme Court cases) beginning on page 959.
Be sure to write down the citation for the case---it will be much easier to look the case up later.