A more thorough explanation:

Law refers to the system of rules and regulations that govern a society. In the United States, the law system is based on common law, which means that judges rely on previous court decisions to make their rulings. This collection of decisions is called case law. Other countries, such as Japan, have a civil law system that relies on explicit codes to make decisions.

Law can also refer to state and federal laws, which include both common law and statutes and regulations. Procedural law outlines the steps that must be taken in legal proceedings, while substantive law defines the rights and obligations of individuals and organizations.

International law is a set of rules that all countries agree to follow out of a sense of mutual obligation and concern. Examples of international law include treaties, conventions, and agreements between nations.

For example, if a person is accused of a crime in the United States, the judge will look at previous court decisions to determine how to rule on the case. The state and federal laws will also be taken into account. Procedural law will dictate how the trial proceeds, while substantive law will determine the person's rights and obligations. In international law, countries may agree to follow a treaty that outlines how to handle a specific issue, such as trade or human rights.