The most commonly used guide to legal citation styles is The Bluebook. Copies of Bluebook are available in Pfau Library. If you are trying to cite legal materials in an academic paper, both APA and MLA style generally follow Bluebook style for those materials.
For a detailed guide online, see LII: Basic Legal Citation, which is based on Bluebook.
Most citations for statutes follow a basic pattern:
Abbreviated name of code, section number (indication of publisher/currency)
The special symbol § substitutes for "section." Indications of publisher/currency are not always included (leave them off if you don't know them).
Some examples for California Code:
Cal. Com. Code § 1101 (Deering 2010)
Cal. Civ. Code § 4100
A major exception to this rule is U.S. Code, whose pattern is:
Title number, Abbreviation, Section number (indication of publisher/currency)
Examples for U.S. Code and U.S. Code Annotated:
15 U.S.C. § 1601 (West 2011)
24 U.S.C.A. § 411
Citations for court opinions follow this basic pattern:
Party name v. party name. Volume number, abbreviated title of source, starting page number (indication of jurisdiction/year)
Indications of jurisdiction are not always included; jurisdiction usually appears on Federal court citations.
Example, U.S. Supreme Court:
Brown v. Board of Education of Topeka, 347 U.S. 483 (1954)
Example, Federal District Court:
Natural Res. Def. Council v. Fox, 93 F. Supp. 2d 531 (S.D.N.Y. 2000)
(In the example above, S.D.N.Y. stands for the jurisdiction, "Southern District, New York.")
Example, California Supreme Court:
People v. Cole, 33 Cal.4th 1158 (2004)
As public documents, court opinions have historically been reprinted in a variety of sources. One of these is usually the official reporter of decisions for that court, while the others are usually from commercial publishers who may add material such as notes and research content. For this reason, a case name is sometimes followed by several "parallel" citations to all the places it has been printed, in order of official weight.
This is most commonly seen on U.S. Supreme Court citations:
Brown v. Board of Education of Topeka, 347 U.S. 483, 74 S. Ct. 686, 98 L. Ed. 873 (1954)
In this example, U.S. stand for the official reporter, the United States Reports. S. Ct. stands for Supreme Court Reporter, and L. Ed. stands for Lawyer's Edition, both reprints by the West publishing company.
An example from California:
People v. Rogers, 5 Cal.3d 129, 95 Cal.Rptr. 601, 486 P.2d 129 (1971)
In general, only the citation to the official reporter is required, and the parallel citations are optional.