Okay kiddo, sometimes countries want to help each other out by sending soldiers to another country to keep the peace and make sure people are safe. This is called an international security assistance force (ISAF).
ISAF is made up of different countries' soldiers who work together to make sure a certain place is safe. They might have to do things like patrol the area or make sure there aren't dangerous things like bombs around.
When countries agree to help out with ISAF, they work together under one leader. This leader makes sure everyone is doing their job and things are being done the right way.
ISAF is important because it helps countries work together to make sure everyone is safe and can live their lives without fear.