The "Laws.." book contains the definition of the 17 laws.
The "Advice.." book explains how the laws must be applied on the field. It includes situations and examples. It is written in an easy to understand language. Also, all Certification test questions are written verbatim from the "Advice..." book; so, if you want to get a higher grade in your Recertification test, and increase the chances to be a quality referee, you should also study the "Advice..." book. This is a "must have" book.
The "Guide..." book informs you about signals, mechanics, field positioning, prior and during the game. Also procedures during misconduct, substitutions, and other situations are presented.
The "Administrative Handbook" presents committments, policies, Code of Ethics, Certification, Travelling out of state, US Soccer/AYSO Cross Certification and many other admin subjects.
"Referee News" are a set of documents and videos (Referee Week in Review) directly from US Soccer that address particular situations that have occurred on the field. They explain how such situations should be handled by the referee team. There are also key news related to the Referee world.