Well first off I was born into a Christian home. Both my parents are Christians and my Grandparents are Christians on both sides. Because of this, I obviously grew up believing in the Bible. From Sunday school to my parents at home, I was constantly taught Biblical stories and verses and just accepted them as truth. However, as I got older I believed in the Bible not only based on faith but because it is supported by evidence.
The Bible was written by about 40 different authors over a span of more than 1000 years. All of the books of the Bible are connected and have one universal theme and that is of God. Other religions such as Islam have holy books written by only one author (Muhammad). Obviously it is a whole lot easier to just make something up if you are the only one writing it as opposed to 40 different people from different time periods and different languages. There are also over 10,000 known manuscripts of the Old or New Testament. Some of this is a corner of a page, some an entire Bible. The Bible also makes prophecies that come true. The Old Testament (remember this was written up to 1000 years earlier) makes prophecies such as the virgin birth of the Messiah. This of course came true with Jesus in about 4 BC. Other prophecies such as a Messiah from the descendants of King David came true (Jesus was a descendant of David). There are also a number of prophecies about the end times. Lastly, there are secular historical documents from the time period of Jesus that talk about Jesus and him doing miraculous works.
This is not all of the evidence but it certainly points to the Bible being true. The Bible says that All scripture is God breathed and is useful for teaching, rebuking, correcting, and training in righteousness (2 Timothy 3:16). Obviously people will have different view points on all of this but this is why I believe the Bible is truthful and the word of God.