Okay kiddo, have you ever played chess or checkers? If you have, you know that sometimes you need to protect your pieces from being captured by your opponent.
Now imagine that instead of a chess board, there's a big country called China a long time ago. This country wanted to protect its land from other countries that wanted to take over.
In order to do that, the Chinese leaders came up with a plan called the "Three Emperors' Corner". This wasn't a real corner, but instead a way of dividing the country into three parts that would each be ruled by an emperor from a different family.
One of the emperors ruled in the north, another in the southwest, and the last one in the southeast. By dividing up the land this way, it was harder for enemies to conquer the entire country.
Just like in chess, if one emperor was attacked, the other two could come to help him out. This way, China was able to protect itself from invaders and maintain its power for many years.
So that's the Three Emperors' Corner: a way to divide up China so that enemies couldn't conquer it easily and the rulers could help each other out if needed.