For detailed description of how federal laws are made, see the following guide:
Federal Statutory Process
Once a federal law is passed by Congress, it is assigned a law number and legal statutory citation (public laws only), and then published as a slip law. A slip law is an official publication and "competent evidence" of the law.
At the end of each session of Congress, the slip laws are compiled into the Statutes at Large. The Statutes at Large is a chronological arrangement of the laws in order of enactment. The laws published within the Statutes at Large are referred to as session laws.
Every 6 years, public laws are incorporated into the United States Code, which is the codification of all of the laws arranged by subject. Only 25 Titles have been enacted into positive, statutory law. The other Titles are prima facie evidence of the law and the Statutes at Large still govern.
The official text of PA statutes is found in the Pennsylvania Consolidated Statutes (Pa.C.S.). There is also an unofficial annotated version of the statutes, the Pennsylvania Consolidated Statutes Annotated (Pa.C.S.A).
Not all of the statutory titles have been reorganized under the Pa.C.S. For these titles, you must consult Purdon's Pennsylvania Statutes (P.S.).