Regarding the last question: "Why is there so many different versions of the Bible? Why do they keep changing? How reliable is it if other people keep changing them and bringing out new versions?"
It's not so much that there are so many different versions, but so many different translations.
They keep changing because they the language they are translated to changes and because they get revised in an effort to improve the clarity and meaning.
There are also several different methods used to translate the versions.
King James = literal translation (i.e. word for word)
NIV = dynamic equivalence (sense for sense) translation.
The Message = Free translation
In the case of free translations like The Message, they may not be based on the original text but on other translations so their accuracy is open for dispute as there is a lot of interpretation going on.
The original version was written in Hebrew, Aramaic and Greek. If you research the dead sea scrolls which are old copies of various parts of what now makes up the bible you will find out that they are nearly identical to the modern text despite being thousands of years old.