Okay kiddo, so a long time ago there was a really big country called China, and they had an emperor who was like a king. And China was so big that there were other countries nearby that were kind of like little brothers to China.
One of these little brothers was called the Ryukyu Kingdom, and it was on an island near China. The emperor of China thought it was important to keep a good relationship with Ryukyu, so he would send people called missions to go visit them.
The missions were like special groups of people who were chosen to go and represent China. They would bring gifts and talk to the king of Ryukyu to show that China cared about them.
The missions were a big deal because they would have to travel by boat for a really long time to get to Ryukyu. And when they got there, they would dress up in fancy clothes and act really polite and respectful.
Sometimes the missions would even bring things like books, art, and other cool stuff from China to give to the people of Ryukyu. And the people of Ryukyu would also send things back to China, like rare animals and plants.
So that's basically what the imperial Chinese missions to the Ryukyu Kingdom were all about. They were like visits from big brother China to little brother Ryukyu, to show that they cared about each other and had a good relationship.