To answer bluntly: yes, that's how I know.
There are millions of people that believe in God as much as you, but do not follow the bible.
Those millions of people who "believe" in God and don't read the Bible either don't believe in God and just say they do, or they are lacking in common sense. If one believes in God, wouldn't it be a good idea to read the Book He left for us? If one believes in God, shouldn't we try to find out what He wants us to do? Just a thought.
Just because something was written by a human being doesn't mean it's true, especially when dealing with God, who has reign over all.
You are right that because something is written by a human it is not necessarily true. Yes, the Bible was written by humans, but the things they wrote were not their own ideas. Their writing was inspired by God. The New Testament contains the gospels, which is basically a first-hand account of the teachings of Jesus from the people that saw what He did. Much of the Bible is stories of the things that people have seen God do in their lives.
Written by men, yes. True, YES! Why true, you ask? Here's why the Bible can be verified as true. The Bible claims to be the infallible Word of God and has been tested as such by many theologians and historians over the last 2000 years. If it were untrue, they would have figured that out LONG AGO. Even today, archeological finds are proving that events described in the Bible are historically accurate and true.
As a student of the sciences, I am taught to test hypotheses for validity. If a hypothesis stands up to the tests, it can be said to be true. The Bible has stood up to 2000 years of tests. That's good enough for me.
On top of all that is my own personal testimony of the things I've seen in my life that are truly miracles. Just the fact that I am here and able to type these responses to you is due to God acting in my life through the Bible. If I only had the time to tell it all...