Okay, kiddo, in France, an échevin is a person who helps the mayor in running a town or city. They kind of like the mayor's assistant.
The échevins work together with the mayor to make important decisions about things like buildings, streets, and other important stuff in the town or city. They also make important laws that people need to follow.
Think of it like your school, where the principal is like the mayor, and the échevin is like the principal's assistant. They help make sure everything runs smoothly and everyone is happy!