The best overview over this subject is the English Wikipedia entry "International law" and I advise you to read it before the course starts. Basicly we will be dealing with what a nation may or may nor do against another nation. These questions arise every days in the news. Right now, for example, we are in the beginning of a global "trade war". How that conflict is conducted is regulated by the WTO treaty. In May the news where filled with the protests in Gaza and Israels sniper activity. This is regulated by the UN Treaty and the Geneva Conventions. In International Law we mainly look at the rights and obligations of states, and not the rights and obligations of people or companies.