The United States Code is law that was created by the legislative branch of the government. The Code is divided into 51 broad subject areas. You can search by topic, by a code section number (if known) or by simply clicking on the table of contents. It is an unannotated code with just the text of the statutes.
Search for pending legislation, bill analysis and many related materials on these legislature web sites.
The Public Law updates various U.S.C. sections in different titles of the U.S. Code, because this Act deals with many different subjects - banking, immigration, criminal law, transportation, etc.
See Bluebook Rule 18.2.1(a)(i) for information on authenticated documents.