Is John the Baptist the same John who wrote the Book of John in the New Testament? I am confused about whether or not it was St. John the Baptist who wrote the Book of John in the New Testament.  I thought this was a different John who was one of the apostles.
You are correct in that the author of the Gospel of John was definitely not St. John the Baptist, but called himself the "Beloved Disciple", who testified to the truthfulness of the eyewitness account about Jesus and his ministry on earth (John 21:24).

The identity of the Beloved Disciple has been associated with St. John, son of Zebedee, one of the 12 apostles called by Jesus Himself (Mark 3:13-19).  For more on the identity of the "Beloved Disciple", you can read Who Wrote the Gospel of John? written by Dr. Gary M. Burge for the blog of the publisher Zondervan, which is academically responsible, or the wikipedia article.