The "law" is not one body of complete works. Instead, it is several separate collections, one or more of which may apply to any given situation.
The U.S. Constitution: A high-level document that lays out the most important principles for how the U.S. legal system is structured and what authority the various branches of government have to make new laws.
Federal Statutes: The U.S. Congress frequently passes new laws that become statutes.
Federal Cases: Federal courts decide cases about federal law, interpreting federal statutes and sometimes creating rules when needed. They also hear cases between two parties that are from different states.
Federal administrative regulations: Some agencies are created by the U.S. Congress and are part of and overseen by the executive branch. They issue regulations that explain and expand federal statutes, and are part of federal administrative law.
State constitutions: Like the federal government, state governments have constitutions that form the basis of their legal structure.
State statutes: Like Congress, state legislatures pass statutes, which constitute state statutory law. While federal laws apply everywhere, these laws apply only within the state.
State administrative regulations: As at the federal level, agencies are created by state legislatures but overseen by state governors. They write regulations, which constitute state administrative law.
Local ordinances: Local governments pass ordinances that become police codes, building codes, planning codes, health codes, and so forth.
Most times, your legal research will probably touch only two or three of these legal sources.