Okay kiddo, so let's start by talking about who Muhammad was. Muhammad was a man who lived a long time ago in a place called Arabia. He's important because he started a religion called Islam.
Now let's talk about the Bible. The Bible is a book that many people believe is very important. It's made up of two parts, the Old Testament and the New Testament. The Old Testament is mostly about the history of the Jewish people, and the New Testament is mostly about the life of Jesus and his followers.
Muhammad knew about the Bible because many people in his time followed the religion of Christianity, which is based on the teachings in the Bible. However, Muhammad did not believe that the Bible told the whole story about who God was and what God wanted from people.
So Muhammad received messages from God that he wrote down in a book called the Quran. Muhammad believed that the Quran had the complete and final message from God, and that it corrected some of the mistakes that he believed were in the Bible.
For example, Muhammad believed that the idea that God had a son, which is an important part of the Christian Bible, was wrong. He believed that God was one and did not have a son. This is a big difference between what Muslims like Muhammad believe and what Christians believe.
So, in summary, Muhammad knew about the Bible, but he believed that it was not the complete and final message from God. Instead, he believed that the Quran was the complete and final message from God.