Kliros is like a group of people who sing songs in a church or a temple. These people are organized in a special way so that everyone knows which part of the song they need to sing.
Imagine that you and your friends are playing a game where you all have to sing a song together. You decide that one of your friends will sing the first part of the song, another friend will sing the second part, and so on. This way, everyone knows when it is their turn to sing and they can all sing together.
This is how the kliros works in a church. There is a group of people who are trained to sing specific parts of the songs. They are organized in a specific way, so everyone knows their role. This way, everyone sings together, and it sounds beautiful!