Okay, so imagine you and your friend are playing a game of tag. Your friend is "it" and they are chasing after you trying to tag you. But there's a small area in between two houses that you know is really hard to get through, and you can run through there to escape from your friend.
The Brčko Corridor is kind of like that small area between two houses. Brčko is a town in Bosnia and Herzegovina, and the corridor is a stretch of land that connects two parts of the country that are separated by a little piece of land owned by another country.
Without the corridor, it would be really hard to travel between these two parts of the country. But with the corridor, it's kind of like a shortcut that makes it much easier to get from one part of the country to the other.
So just like how you use the small area between two houses to escape from your friend in tag, the people of Bosnia and Herzegovina use the Brčko Corridor to make it easier to travel between two parts of their country.