Okay kiddo, so when someone is born, their parents usually pick a name for them. This name is called their "Christian name" because it is usually given to them when they are baptized in the Christian church.
Now, a Christian name can also be called a "given name" or a "first name". It is the name by which we call a person and it is used to identify them.
Sometimes people may have more than one Christian name, like having a first name and a middle name. This is because their parents may have given them more than one name that they like.
So, in summary, a Christian name is the name that a person is given at birth or baptism and it is used to identify them.