You will be contacted by the advocates of the two parties involved. They will explain and guide you so that you can succeed as a witness. Look into the case handled by the ICJ so that you can state your country’s/organisation’s point of view concerning the case. Remember that you can’t invent facts, if you have none. You need to always speak the truth since you are under oath. If you don’t know something, you just say: ‘I don’t know’.