The Bible was produced as a result of the direct inspiration of God by means of His Holy Spirit. That is the fundamental basis for belief.
2 Timothy 3:16, 17 All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work.
2 Peter 1:19-21 And so we have the prophetic word confirmed, which you do well to heed as a light that shines in a dark place, until the day dawns and the morning star rises in your hearts; knowing this first, that no prophecy of Scripture is of any private interpretation, for prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit.
That is a very small sample of what the Bible says about itself. However, what external evidence is there? There is the stunning evidence of Bible Prophecy, the witness of history and archaeology, the amazing witness of the nation of Israel which brings Bible prophecy to our headlines on a daily basis and, most importantly, the witness of the resurrection of the lord Jesus Christ.
Here are links to information on the website which you will find helpful (please click on the titles):
I hope you have found this helpful.