International law is the system of agreements and treaties between nations that govern how nations interact with other nations, their citizens, and businesses from other nations. There are typically two different types of international law.
Private international law helps to resolve disputes between people or companies who have a connection to more than one country.
Public international law is about the relationships between different countries. These relationships include things like the standards for how people should behave when they're around other countries, the laws about the ocean, economic laws, diplomatic laws, environmental laws, human rights laws, and humanitarian laws.
Some principles of public international law are written down in a series of treaties. Other principles are not written down, but they are followed because nations agree to them.
Since most international law is governed by treaties, it's usually up to the individual nations to enforce the law. However, there are a few international organizations that enforce certain treaties. The most notable example is the United Nations, which has 192 member states.