Traditionally, international law dealt with the relations between states and was frequently referred to as the law of nations or public international law. Universal law is the bundle of rights, duties, privileges, and immunities which are so fundamental to the existence of humans or nations that they vest in these groups without any affirming act being required. General law is the body of law derived from the conduct between states, but requires an affirmative action on the part of a state to be bound by it. Particular law is applicable to a single state because of the conduct and practices of that state. Only recognized governmental organizations can create international law.
States generally use treaties to create international law.
Let s start with a look at researching treaties.