Secondary sources help you identify and understand the law. Secondary sources are not law and are never cited as legal authority. They include legal dictionaries and encyclopedias, journal articles, books, treatises, practice aids, self-help materials, and finding tools.
It is easier and generally more effective to consult a secondary source to find key statutes, regulations, and cases that govern a particular area of law, e.g., family law, probate law, employment law, criminal law, before trying to identify, locate and analyze those same resources using finding tools for statutes, cases, and regulations.