Okay, so you know how sometimes when you play with your friends, you make a pact to always be friends and help each other out? That's kind of like what the Compact of Free Association is.
It's a special agreement between two countries, like the United States and the Marshall Islands or the Federated States of Micronesia or Palau.
The people in those two countries decide to work together and help each other out. The Compact says that the United States will help those countries with things like money, protection and resources. In return, those countries agree to certain things like following certain laws and letting the United States military be there to help protect them.
It's a way for the countries to stay friends and work together for a long time, kind of like your friendship pact with your friends who you always want to be friends with.