Excerpt from LDS.org
Joseph Smith translated the Book of Mormon by the gift and power of God. During the process of dictating, transcribing, copying, typesetting, and printing, some human errors were made. Soon after the first printing of the Book of Mormon, in 1830, readers began finding typographical, spelling, and other mistakes. The Prophet Joseph Smith and Oliver Cowdery made over 1,000 corrections for the second edition (1837). For the third edition (1840), Joseph Smith made further corrections after careful prophetic review, comparing the original manuscript with the printed text.