CHXIV, State of Sept. 15, 1789, 1 Stat. 68-69
= Chapter 14, Department of State established on September 15, 1789, Statute Book 1, section 68-69.
Explanation: "ch" is a common abbreviation for "chapter". "XIV" is the number 14 in Roman numerals. The United States Department of State was established on September 15, 1789.
USC
= United States Code
The United States Code is a collection of legal codes [books] which contain the federal laws passed by the United States Congress.