The Articles of Confederation were the first constitution of the United States. They were created in 1776 but were altered between then and when they were ratified in 1781. The most important fact about the Articles of Confederation is that they created a very weak federal government. The states were not eager to give up power to a federal government that might (they feared) abuse them in the same way that the British government had.
However, the states did want to join together in a loose grouping. They wanted to make foreign policy as a whole nation. This is what Article 9 is about.
Article 9 gives Congress the power over most aspects of foreign policy. It gives it the sole right to declare war. It gives Congress the sole right to send ambassadors to other countries and to make treaties with other countries. It allows Congress to give letters of marque to privateers, allowing them to legally attack ships from other countries. It allows Congress to be in charge of holding trials for pirates. In other words, Article 9 is mostly about giving Congress power over foreign policy for the new United States.