Summarize this article in one sentence.
When questions and conflicts arise in the relationships between sovereign nations, they are solved under the rules of public international law. This body of law consists of the treaties and legal decisions interpreting those treaties.  International law assumes that all the parties, as sovereign states, are equals. Conflicts arising under public international law can be settled either through diplomatic negotiations or in the International Court of Justice. This is the court of the United Nations. Fifteen judges, elected by the UN General Assembly, use international legal precedent to issue advisory opinions and solve legal disputes between governments.  The International Court of Justice has jurisdiction in two types of cases. The first is where the two countries agree to submit the conflict to the court. The second is when a treaty specifies the court as the legal authority over disputes. When citizens of different states have a legal dispute, there is often a question about what law applies. This choice of law question in civil issues, ranging from contracts to family law, is discussed in the Hague Conference on Private International Law. In general, courts will first defer to any contract or agreement clauses that identify what courts will have jurisdiction. In the absence of explicit choice of law language, the court will look to the overall circumstances of the contract, the behavior of the parties in creating the contract (called parol evidence) and if the parties can agree on jurisdiction. The customary international law is codified in the Vienna Convention on the Law of Treaties. Under this custom, states consistently adhere to certain practices out historical and legal obligation.

Summary:
Understand the concept of public international law. Differentiate private international law from public. Review the sources of international law.