The Book of Ether is Moroni's abridgment of the 24 plates found by King Limhi's people (Mosiah 8). It starts at the creation of the world, but Moroni skips all that and starts at the Tower of Babel with a guy named Jared. Jared's brother was a man of God, so when the languages got confounded, Jared asked his brother to pray that their language wouldn't get confused. He did, and God granted that to him. Then God promised to bring their families to a choice land and make a mighty nation out of them.