There are 51 titles (or subject areas) in the United States Code, each including a number and a subject title.
All the statutes for that subject area are included in that title. For example, all the bankruptcy statutes are included in Title 11 of the United States Code. The title number is the first number of a statutory citation. Thererfore, the statute outlining a debtor's duties under the Bankruptcy Code is found at 11 U.S.C. 521.
When citing to a Federal statute, the first number is always the title number.