The United States Statutes at Large are the official source for the session laws of the United States Congress. This means these are the laws passed by Congress in the order in which they were passed, exactly as they were passed and before they were re-arranged topically for inclusion in the United States Code.
Typically if you're using the Statutes at Large you already have a cite in this form: 123 Stat. 1704. This means you're looking for volume 123 in this set and page 1704. There will probably be an accompanying Public Law number with your citation: Pub. L. No. 111-23. This means "the 23rd law passed by the 111th Congress."
To see how to cite to the Statutes at Large check out ALWD Rule 14.7 and Bluebook 12.4.