A good place is to start searching in LexisNexis. But, if you want to see the original law passed before 1989, you will have to consult the paper copy or the American Memory site.

There are two numbering systems for laws:

1. Public or private law , Congressional session, number. For example, P. L. 108-45 "Strengthen AmeriCorps Program Act" is the 45th public law passed during the 108th Congress.

2. Volume STAT. page number. This is used mainly in the paper copy. For example, 117 Stat. 844 "Strengthen AmeriCorps Program Act" is located in volume 117 of the Statutes at Large on page 844.

LexisNexis Congressional: Legislative Histories, Bills and Laws Select Public Laws. You can search back to 1989.

American Memory (Library of Congress): Statutes at Large (1789-1875) contains online full-texts of the laws passed during each Congress in the years given.