Okay kiddo, so you know how Christians have a holy book called the Bible, right? Well, the Bible is actually made up of many different parts, like stories, teachings, and letters from a long time ago.
Now, people didn't just magically agree on which parts should be in the Bible. It took a lot of debating and discussing and thinking to figure it out. And even then, different groups of Christians have slightly different Bibles!
But the basic idea is that the books in the Bible were chosen because people thought they were really important for teaching about God and Jesus and how to live a good life. So they put them all together in one big book, which we call the Bible.
Does that make sense, kiddo?