It is important to remember the hierarchy of American law. Cities can make laws, but these laws must be in compliance with the law of the State in which that city is located. Each of the fifty states make laws, but these laws must be in compliance with federal law. Federal law is therefore supreme.
Federal law is made by each of the three branches of government:
It is usually easy to find U.S. law; the hard part is interpreting the law. To help you understand the law, there are numerous secondary sources with descriptions and analyses of the laws. Some of these include legal encyclopedias, nutshells, hornbooks, treatises, practice guides, and law journals.
The UC Law SF Library has an extensive collection of both the primary sources of American law (regulations, public laws, and case law) and the helpful secondary sources which explain the law.
The Law Library of Congress webpage is a good starting place for students unfamiliar with the U.S. legislative process. It includes information about how U.S. laws are made and a brief guide to the U.S. legal system.
The following five books are good places to start if you want to get a better understanding of the American legal system. They are very readable and don't go into so much detail as to be overwhelming:
An Introduction to the Legal System of the United States, 3rd ed.
By E. Allan Farnsworth
KF387 .F3 1996 (5th Floor)
Introduction to the Law and Legal System of the United States
By William Burnham
KF385 .B87 2002 (5th Floor)
Introduction to the Law of the United States
By David S. Clark
KF385 .I58 2002 (5th Floor)
Law in the United States: An Overview
By Peter Hay
KF385 .H313 2002 (5th Floor)
Legal English: An Introduction to the Legal Language and Culture of the United States
By Teresa Brostoff
KF272 .B76 2003 (5th Floor)