Okay kiddo, have you ever done something bad and then felt really sorry about it? Well, that's kind of like what atonement is. It means making up for something wrong you've done.
In some religions, like Judaism and Christianity, atonement is an important part of asking for forgiveness from God. For example, if you do something bad, you might say sorry to God and do something good to make up for it.
Sometimes, people also make atonement to other people. If you hurt someone's feelings, you might say sorry and try to make them feel better by doing something nice for them.
Overall, atonement is about making things right after you've done something wrong. It's a way to show that you're sorry and to try to make things better.