When people talk about the New Testament of the Bible, they're talking about a collection of writings that were put together hundreds of years ago.
Long ago, there were many people who wrote things about Jesus and his followers. Some of these writings were true, and others weren't.
So, a group of very smart people got together and decided to pick out the writings that they thought were the most important, and put them all together in one book. They did this because they wanted to make sure that people had a good understanding of what Jesus and his followers were all about.
These smart people spent a lot of time reading and talking about all the different writings. They decided which ones made the most sense and which ones were closer to the truth.
Eventually, they picked out 27 writings that they thought were the best, and those writings became the New Testament that we have today.
So, that's how the New Testament was put together- lots of smart people coming together to decide which writings were the most important and true.