Why do people say the bible is their final authority?

Many people believe what they hear but when it comes to God and his warning of false teachers, I am learning to question the majority of what they say. I am reading a website that says the bible is their final authority in all matters of faith and practice. How is this even possible? The bible is just a book. It is not the living God. When studying the Bible we need to ask for knowledge, wisdom, and understanding. Do you guys even know how the bible was created? True scripture is simply the people of God writing down several things concerning God. The bible is filled with signs and wonders, history, teachings, and the words of God. So, how is the bible the final authority? Are you guys telling me that a child of God cannot come and add to the scriptures? What if God speaks to them and tells them to right it down? Isn't there more history to be known? What about all the prophecies from God? What about the teachings and commands from the holy spirit? Well, the bible may be your final authority but I want God himself to be mine. Grace be with you.