Federal regulations result from the power granted to agencies of the federal executive branch to put in place rules and policies that have the force of law. There is a process. For most regulations, the responsible agency:
Announces a newly-proposed regulation or regulation change in the Federal Register,
The rules published in the Federal Register are codified in an annual set called the Code of Federal Regulations (CFR) and into the eCFR --- a currently but not officially updated version. The CFR is a compilation of regulations; that is, older material is updated to reflect newer regulatory decisions. These two titles are used as complementary; a regulation announced for comment may be completely new but often serves to update existing regulations. Likewise, regulations in the CFR may have been updated by actions reflected in the Federal Register.
The CFR is divided into 50 titles (or subject areas) of federal regulation. Each title is divided into chapters, which are assigned to the agencies that issue regulations pertaining to that subject area. Each chapter is divided into parts; each part is then divided into sections.