Okay kiddo, so Mark 7 is something called a "chapter" in a book called the Bible. The Bible is a big book that tells stories about God and people who believed in God a long, long time ago. Mark is one of the names of the people who wrote about Jesus and what he did when he was on Earth.
In Mark 7, Jesus is talking to some people who are very religious and follow a lot of rules. Jesus tells them that sometimes they care too much about following rules and they forget about being kind and loving to other people. Jesus says that it's not what goes into your body (like food) that makes you a good person, but what comes out of your heart (like being kind, forgiving, and not being mean to others).
So basically, Mark 7 is a story about how being a good person is more important than just following rules all the time. We should be kind and loving to others, because that's what God wants us to do.