How legal systems work

Where rules come from.

Sources of law

Constitutions sit at the top, then statutes passed by legislatures, then regulations made under them. In common law countries, decided cases also bind later courts.

Common law systems rely heavily on precedent; civil law systems on codes.
Courts interpret statutes, and that interpretation becomes part of the law.

Jurisdiction

Which country's law applies, and which court can hear the case, are separate questions decided before the merits. Online activity makes both harder.