A replica of the golden plates given to Joseph Smith Jr.on display at the Hill Cumorah visitor center in Palmyra New York.
The Mormon.org site describes the encounter as follows:
In September 1823, Joseph Smith was visited by a heavenly messenger named Moroni, in the same way that angels often appeared to Church leaders in the New Testament (see especially the book of Acts). He informed Joseph that God had a work for him to do. Moroni told Joseph that a record of the ancient inhabitants of the American continent was buried in a nearby hill and that the record contained the fulness of the gospel of Jesus Christ.
In September 1827, Joseph received the record, which was written on thin plates of gold. We now know it was not uncommon for people from the era of ancient America to keep records on metal plates. Joseph translated the book into English by the inspiration of God. The book is called the Book of Mormon: Another Testament of Jesus Christ It is named after Mormon, an ancient prophet who compiled the sacred record. The book verifies, as another testament of Christ, the reality and divinity of Jesus Christ. It is, then, a second witness that affirms the truth of the Bible. The Book of Mormon was published in 1830. Since that time it has blessed the lives of millions of people through its powerful message about Jesus Christ and His gospel.