In short, the Bible is divided into two main parts, the Old Testament and the New Testament.  Each testament is comprised of many books, which were divinely inspired by God, but written by humans.  The Old Testaments is the period prior to Jesus' birth that tells our faith history,  and tells us of the upcoming Savior/Messiah.  The New Testament recounts some of the many deeds and teachings of Jesus.  In addition, we learn from the people that were closest to Jesus of his precious love and guidelines for living in a Godly way.

To find out what John 3:16 says in the Bible, you need to find out where the Book of "John" is located.  All Bible have indexes in the front.  The indexes are usually split between the Old and New Testament.  Once you have located the book of John in the New Testament, you look for the number that is next the book's name, in this case it is the number "3".  The "3" indicated the chapter of the book.  The chapters numbers are clearly stated in the Bible.  The number following the "colon" indicates what verse or verses are being cited.  In the case, we are citing the 16th verse.  Each thought/verse in the bible has been numbered and those numbers appear in the Bible text.  So in our case, we have cited the 16th verse of the 3rd chapter of the Book of John.  If you look it up that verse will read something like this:  For God so loved the world that he gave his only Son, that whoever believes in him should not perish but have eternal life.

There are a few books titles that seem to repeat themselves for example there is "John", "1 John", "2 John",  "3 John", these are all different books and are listed separately.