When doing Legal Research for undergraduate study follow this path:
Students and Practitioners
Students write papers about all sorts of topics concerning law such as gun control, abortion and health care. Background sources and books will give you an overview and cite key cases and codes. Law Reviews articles will explore specific topics of the law in depth and also point to key cases and codes (in Nexis Uni, you can link out to them from the article).
Practitioners must understand how case law has been treated over time and use Westlaw or LexisNexis to find new case law; they check the treatment of the cases in court by checking KeyCite or Shepherds. This is because cases can set a precedent that must be followed.
Stare Decisis (stair-ee di-sahy-sis) Latin for "to stand by things decided"
Here is an entry in Ballentine's Law Dictionary. The system of precedence -- building a case on decided case law -- drives the legal research of practicing lawyers. You are looking for other cases on the points of law of your case in order to support your postilion; you need to know how those cases were treated in court: affirmed, overturned, etc. (Shepard's, KeyCite). It is part of America's common law legal system; other countries apply a civil law legal system. Since the Supreme Court is our highest court, all lower courts must follow decision cited by it. Access to the latest case law is essential.
393 U.S. 503 Tinker v. Des Moines School District (1969)
If you visit the Cornell Law Library and needed to look up this print case, you would first find where the United States Reporter volumes sat on the shelves. Once there, you would see that all the volumes were numbered and you'd look for volume 393; finally, open the book and you would turn to page 503. The basic legal citation style is Volume - Name of the Reporter - Page Number.
Most lawyers and law schools use the Harvard Bluebook to cite the law. A copy is available at the library's Research Help desk. The free citation manager Zotero can format citations in the bluebook style. Case law found in Google Scholar's case law downloads nicely into Zotero. Chicago style refers to the Bluebook style for legal citations and can be assigned for legal studies courses; check with your professor to be sure. I can help you with Zotero; make an appointment with me and bring your laptop.
Legal Reporters: Governmental versus Commercial Publishers
While the government issued version of a reporter is often the "official" one to cite to, lawyers began using Westlaw and LexisNexis for two reasons: 1) cases were issued more quickly and 2) the commercial publishers has added value information; they would summarize the case, and annotate them as headnotes so that similar cases on specific points of law can be found. Since the 1990s, a lot of government information has moved online. A new commercial source is Bloomberg Law (introduced in 2009). There are still older sources -- or specialty reporters -- that you may need to go to a law library for, but you should be be able to get most state and federal sources online. Nexis Uni and Westlaw Campus are databases designed at a lower cost -- and with slightly different features -- for the academic markets. I tend to use Nexis Uni (a LexisNexis product for the academic market) for law reviews, legal news, and finding case law. We don't subscribe to Westlaw Campus. I tend to use governmental sites such as FDsys, Congress.gov and state governmental sites to browse through codes and regulations; visually seeing where a code or regulation falls in the body of law can be helpful.
Not every case that is tried gets reported -- only cases that have precedent are reported (yet now there are volumes of unreported cases).
For local cases (cities, counties) you can check the court's website or contact the Clerk of the Court.
Another important thing to know when searching for a law is the jurisdiction. If it is a barking dog, it may be in a local ordinance. If it concerns a drivers license or REAL ID, it is a state law. If it concerns the United States or is interstate, it may be a federal law tried in federal courts. Sometimes it involved multiple jurisdictions (legalizing marijuana has some conflicts between federal administrative and state laws; there have been conflicts with municipal broadband). Additionally, most states have case reporters, but case law also appears in regional reporters. The more you read about it in secondary sources -- background articles and newspapers -- the clearer it becomes.
Civil and Criminal Cases
Is it a civil case or a criminal one? Is an offense against the criminal laws of government or another person? How severe is the crime? When searching trial courts on the state level, they often divide the decisions into civil and criminal. The way cases are handled are often determined by rules of court for either civil or criminal courts. Here is a page on the Rules of Practice and Procedure from the US Courts website.
Additionally, there are numerous open access (free online) sources to explore. Wikipedia is one place to go to find where an Act has been codified in the United States Code (see the Codification sections in the sidebar of this entry for the Telecommunications Act, for example; there is also the Table of Popular Names in Cornell's Legal Information Institute. If you are looking up a Supreme Court Case, the Oyez website is a terrific place to find the case summary, how the court voted on a legal question, and it even includes oral transcripts. Where you go depends on your information need; there is self-help law (you have a personal legal issue such as creating a will), there is information about legal interpretation (how is gun control case law interpreted by the courts? ), and then there is applying the law as a practicing lawyer. Practitioners have the burden of needing to know the most current codes (any new amendments), the most current cases, as well as how cases have been treated in court (using Shepard's or KeyCite).
NOLO press offers self-help legal guidance to specific topics of law -- everything from estate planning to landlord -tenant issues. To dive into a new area of legal practice, try a volume from West's Nutshell series; they are short and brief primers to areas of law. If you are headed to law school, a hornbook can be useful; they tend to be expensive and undergo many updates to keep up with new case law.