Primary sources are the law itself. They are created by Federal and State branches of government.
Statutory Law: Statutes, codes, constitutions, rules of court. Generally, laws passed by Congress.
Case Law: Decisions of courts and administrative bodies (e.g., Federal Court of Appeals, Supreme Court of the State of New York)
Administrative Law: Rules and regulations promulgated by government agencies (e.g., EPA, OSHA, NJ Department of Education)
Secondary resources are a good starting point for legal research.
They give background information and a general discussion of legal topics, and include seminal cases on the topic.
Secondary resources include, among others: law review articles and legal encyclopedias.
A law review article analyzes a legal issue and references statutes and cases, often with links to the full text.