Short answers, pulled from the story.
Law is a set of rules created and enforced by governmental or societal institutions to regulate behavior, though its precise definition remains a matter of longstanding debate. It has been described both as a science and as the art of justice. H. L. A. Hart called it a system of rules, while John Austin called it the command of a sovereign backed by the threat of a sanction.
In civil law systems, a legislature or central body codifies and consolidates the law, and judges decide each case afresh from the State's laws. In common law systems, judges make binding case law through precedent, or stare decisis, where decisions by higher courts bind lower courts. Modern scholars argue the significance of this distinction has progressively declined.
The Sumerian ruler Ur-Nammu formulated the first law code by the 22nd century BC, consisting of casuistic if-then statements. Around 1760 BC, King Hammurabi codified Babylonian law and inscribed it in stone as stelae across Babylon, a work known as the Codex Hammurabi.
Donoghue v Stevenson arose when the decomposing remains of a snail floated out of an opaque ginger beer bottle in a cafe in Paisley, after which Donoghue fell ill with gastroenteritis. The House of Lords held the manufacturer liable, and the case established the four principles of negligence in tort law.
Public law concerns government and society, including constitutional law, administrative law, and criminal law. Private law deals with legal disputes between parties in areas such as contracts, property, torts, delicts, and commercial law. This distinction is stronger in civil law countries than in common law jurisdictions.
Religious law is explicitly based on religious precepts and scriptures. Its main examples are the Jewish Halakha and Islamic Sharia, both of which translate as the path to follow, along with Christian canon law. The Catholic Church has the oldest continuously functioning legal system in the western world.
From 529 to 534 AD, the Byzantine Emperor Justinian I codified and consolidated Roman law into the Corpus Juris Civilis, reducing it to one-twentieth of the earlier mass of legal texts. Rediscovered in 11th-century Italy, this work became the basis from which modern civil law systems essentially derive.