Law is defined as a "...body of rules and principles governing the affairs of a community and enforced by a political authority; a legal system".
On the Federal Level there are two types of Laws: 1) Public and 2) Private.
Public Laws are laws which apply to the country as a whole. They are designated as P.L. Congress- law number. Public Law numbers are assigned chronologically within each Congress. Public Law numbers bear no relationship to bill numbers. For example P.L. 104-10 is the 10th law passed by the 104th Congress.
Private Laws are laws which benefit a single person or organization. Private laws are designated as Private Law Congress-law number. Private Law numbers are assigned chronologically within each Congress.
Public and Private Laws are issued first as Slip Laws and later bound in the Statutes at Large. The first official version of a new law is the Slip Law. Ultimately all public laws make their way in the United States Code, a codification of all laws currently in force.
Once a law is on the books, it is up to Executive Branch of the government and its agencies to enforce them. These agencies establish rules and regulations - the Administrative Law (Regulations) - detailing the enforcement process. These regulations have the force of law and are disclosed first in the Federal Register and later incorporated into the Code of Federal Regulations.
Between the time a bill is first proposed and being signed into law by the president, it undergoes careful study by both the House and the Senate. Committee hearings are convened, debates are held, votes on various versions are conducted, etc. Each of these steps generates a paper trail. The following is a simplified life cycle of a bill and some of the documents associated with each stage.
Legal research is as simple and as complex as following the paper trail.
Legislative History Research Guide. (Georgetown University. Georgetown Law. Georgetown Law Library)
Researching Federal Statues. (Library of Congress)
Thurgood Marshall Law Library Guide to Legal Research, 2014-2015. (University of Maryland. Francis King Carey School of Law)
Enactment of a Law. Thomas. The Library of Congress. (By Robert B. Dove, Parliamentarian, United States Senate)
How Our Laws are Made. Thomas. The Library of Congress. (Revised and updated by Charles W. Johnson, Parliamentarian, United States House of Representatives)
How Our Laws are Made - Learn About the Legislative Process. (CONGRESS.GOV Resources)
Kids in the House: How Laws are Made. (Office of the Clerk)
Legal Research: How to Find & Understand the Law. 14th Edition. Stephen Elias and Susan Levinkind. Berkeley, California: Nolo, 2007. Guide that explains how to do legal research, including developing search terms and strategies, online research, understanding legal resources, etc.
The Legislative Process. (United States House of Representatives)