Okay, so imagine you and your friends all love a game called "Tag". You all live near each other and play Tag all the time. Sometimes, you even have little competitions to see who is the best at playing Tag.
Now, imagine that there are lots of other kids who also love to play Tag in different neighborhoods nearby. You don't know them very well, but you have heard that they're really good at playing Tag too. But, you don't get to play with them because they're too far away.
So, one day, all of the kids who love Tag decide to join together and make a big group called "The Tag Union." Now, you and your friends can play with all the other kids who also love Tag. You can share tips and tricks, and maybe even have bigger competitions with even more players.
The Arab Union is kind of like that. It's a group of countries who are all located near each other and who have decided to work together. They share ideas and resources, and sometimes they even have big meetings where they talk about how to do things better. Just like you and your friends, they are stronger when they work together than when they work alone.