There are a number of tax sources and they can be confusing to someone new to the field. The friendly folks from CCH (Wolters Kluwer CCH, a legal publisher), have put together a series of tutorials to help you wade through everything.
There are five lessons:
Overview of Sources of Federal Tax Laws (13:33)
Federal Statutes and Legislation (16:22)
Treasury Regulations (14:06)
Judicial System (12:02)
IRS Rulings and Pronouncements (21:16)
You have the option of either listening to the tutorial, or reading the PDFs with the same information.
These CCH tax law tutorials are designed to help tax practitioners learn about tax law and the hierarchy of federal tax law sources, such as the Internal Revenue Code (IRC) and IRS rules.