The Prophet Joseph Smith’s own words about the coming forth of the Book of Mormon are:
“On the evening of the … twenty-first of September [1823] … I betook myself to prayer and supplication to Almighty God. … While I was thus in the act of calling upon God, I discovered a light appearing in my room, which continued to increase until the room was lighter than at noonday, when immediately a personage appeared at my bedside, standing in the air, for his feet did not touch the floor. He called me by name, and said unto me that he was a messenger sent from the presence of God to me, and that his name was Moroni; that God had a work for me to do;
He said there was a book deposited, written upon gold plates, giving an account of the former inhabitants of this continent, and the source from whence they sprang. He also said that the fulness of the everlasting Gospel was contained in it, as delivered by the Savior to the ancient inhabitants;
Also, that there were two stones in silver bows—and these stones, fastened to a breastplate, constituted what is called the Urim and Thummim—deposited with the plates; and the possession and use of these stones were what constituted Seers in ancient or former times; and that God had prepared them for the purpose of translating the book.
For the complete record, see Joseph Smith—History, in the Pearl of Great Price, and History of The Church of Jesus Christ of Latter-day Saints,volume 1, chapters 1 through 6.