Okay kiddo, have you ever heard of the years on the calendar? You know, like 2021, 2022, and so on? Those years are called "Common Era" or "CE" for short.
Now, way back in history, people used a different way to count the years. They used a system called "Before Christ" or "BC" for short. But not everyone in the world believed in the same religion as the people who used BC, and some people didn't like using a religious term to count the years.
So, to make things more fair for everyone, people started using the term "Common Era" instead of "BC". This way, everyone could use the same term no matter what religion they believed in, and it didn't have any religious meaning.
It's basically just another way of saying the same thing as BC, but without any religious association. It's like saying "happy holidays" instead of "Merry Christmas" so that everyone feels included, even if they celebrate different holidays.