The Book of Mormon is composed of the following books which are divided into chapters and verses similar to the Bible:
1 Nephi begins in ancient Jerusalem around 600BC, at roughly the same time as the book of Jeremiah in the Bible. It tells the story of Lehi, his family and several others as they are led by God to travel from Jerusalem to the Americas. 1 Nephi - Omni recount the group's dealings from around 600BC to around 130BC, in which they grow to a sizeable number, and eventually split into two groups, the Nephites and the Lamanites.
The Words of Mormon, written in AD 385, is a short introduction to the books of Mosiah, Alma, 3 Nephi and 4 Nephi. Mormon compiled The Book of Mormon (thus the name). He included the original records comprising 1 Nephi - Omni, then abridged a large quantity of collected records detailing the national history from the end of Omni until his own time.
3 Nephi contains an account of the visit of the glorified, resurrected Jesus Christ to the Americas after his ministry in Jerusalem. Here he gives much of the same instruction given in the Gospels of the Bible, and establishes an enlightened, peaceful society which endures several generations.
Mormon is an account of the events which occurred during Mormon's life, after the enlightened society of 3 and 4 Nephi had deteriorated yet again into warring groups.
Ether is another abridgement by Mormon, this time of the records of a much earlier civilization beginning at the time of the tower of Babel. In this account, a man named Jared, his family and others were led by God to the Americas before the languages were confounded and formed a civilization long before Lehi's family arrived. Mormon placed this account after the end of his own work, before turning over the record to his son Moroni.
Moroni witnesses the final destruction of his people and the idolatrous state of the remaining society. He adds a few spiritual insights and mentions some important doctrinal teachings, and ends the book with an invitation to pray to God for a confirmation of the truthfulness of the account.
The original record was engraved on thin sheets of gold and bound with rings at one edge, much like a modern book. At the end of Moroni's ministry (around AD 421), he hid these gold plates along with several other artifacts in a stone box.
In 1823, Joseph Smith was directed by God to the place where the plates were stored. He was not immediately allowed to take them, but was eventually entrusted with them. With God's help he was able to translate the characters (described in The Book of Mormon as being a variant of Egyptian) into English.
The gold plates were quite heavy, and were consequently much sought-after by those monetarily inclined. Church history records many attempts by others to find and take the plates from Joseph Smith.
Joseph was allowed to show the plates to several people, and these accounts are recorded in the front of The Book of Mormon as "The Testimony of Three Witnesses" and "The Testimony of Eight Witnesses". After translation was complete, an angel received the plates from Joseph Smith, and no public account of their whereabouts has been made since.
Some of the witnesses later signed affidavits attesting that they lied about the authenticity of the plates. However, one of these people on their deathbed claimed that he was paid to claim the plates were false. (looking for documentation on his name, read it in a few places)
Various alternate explanations for the origin of The Book of Mormon have been proposed that are contrary to the offical history of the LDS Church. These include:
There have been changes in wording of the text of the Book of Mormon since it was initially printed.
After the church reported that black men would be permitted to enter the priesthood, on June 9, 1978, a change was made in the 1981 printing of the Book of Mormon. In 20 Nephi 30:6, which formerly said:
the word white was replaced with the word pure. Lists of the changes since the first printing can be found numerous places online, and Project Gutenberg has the text of an early edition which can be compared with current editions.
These textual changes to the Book of Mormon are often presented by its critics as proof of changing doctrines within the church, or of the imperfection of the book as a scriptural foundation.
The church considers this to be invalid because they believe that the church's doctrines are established and sustained by repeated affirmation by its leaders, not by isolated passages of scripture. It also claims that the changes were a "correction" as indicated by the inclusion of this notice in the 1981 edition: