Customary international humanitarian law is a set of rules that tell us how to treat each other during times of war. It says that we must try to protect innocent people, like children and old people, and that we must try to limit the damage and suffering caused by a war. It says that we must not attack hospitals, schools, churches and other important places that might be used by people who are not involved in the fighting. It also says that we must try to help those who are injured and not cause them any more harm or suffering.