Ok, here is where things might start to get a little confusing. The next few chapters of Mosiah contain some really great spiritual information, but also a pretty complex subplot of people moving around and going to different places. I will try to explain it, but a good way to get a basic explanation would be to go to scripturestories.lds.org and look at Chapters 13 through 17.
When King Benjamin was finished teaching his people, he had the names of all of the people who “had entered into a covenant with God to keep his commandments” written down, so that the church would have a record of its members; and also, I would guess, as a sort of census. His son Mosiah then began his reign, and Benjamin died.
King Mosiah wanted to know what had happened to a group of people who had left Zarahemla (the Nephite capital city) and gone to live in the land of Lehi-Nephi, which was the original land of Nephite possession, so he sent a group of sixteen men to go looking for them. The group ended up getting lost in the jungle, so they decided to camp after forty days of wandering. The leader of the group, Ammon, decided to take a few of his men and go check out the city below them. As they were wandering around the outside of the city, they met the king of the land, who had them promptly thrown in jail. After two days, they were brought before the king, who demanded to know who they were. After being told that they were from Zarahemla, the king rejoiced and said that his name was Limhi, and he was a grandson of the man who had originally taken off from Zarahemla.
Limhi tells Ammon the sad tale of his people. The story is told in more detail in chapter nine, but I will tell you the basics. Limhi’s grandfather, Zeniff, was a spy for the Nephite army, and while doing his job, he saw the Lamanites living in the land of Nephi, the original lands of the Nephites. Zeniff and about half of the army wanted to negotiate with the king of the Lamanites to allow them to live there, and the other half realized that that was a bad idea. They had a big internal skirmish, and most of the entire army was killed. The survivors returned to Zarahemla, and Zeniff got as many people as he could to follow him back to the land of Nephi.
Zeniff negotiates a treaty with the Lamanite king, who gives the people of Zeniff two of his cities (does the gift of two whole cities without any payment in return, by your sworn enemy, sound at least a little fishy to anyone else?). They live in peace for a while, and then the Lamanite king decides to come put the people of Zeniff in bondage, by force. Zeniff is a man of God, and instructs his people to pray for strength, and they are able to beat the Lamanites back multiple times.
Keep in mind that the occurrences during the time of Zeniff happened at about the same time that the first king Mosiah was alive, during the latter half of the book of Omni.
I am going to quickly leave the story of Zeniff and return to the story of Limhi meeting Ammon.
After talking with Ammon, Limhi calls his people together to call them to repentance. He reminds them of their sinful ways, and calls them to repentance, and a remembrance of the good things that the Lord has done for them and for their ancestors. His people are in bondage (more on that later), yet he still says:
“O ye, my people, lift up your heads and be comforted; for behold, the time is at hand, or is not far distant, when we shall no longer be in subjection to our enemies, notwithstanding our many struggling, which have been in vain; yet I trust there remaineth an effectual struggle to be made. Therefore, lift up your heads, and rejoice, and put your trust in God, in that God who was the God of Abraham, and Isaac, and Jacob; and also, that God who brought the children of Israel out of the land of Egypt, and caused that they should walk through the Red Sea on dry ground, and fed them with manna that they might not perish in the wilderness; and many more things did he do for them. And again, that same God has brought or fathers out of the land of Jerusalem, and has kept and preserved his people even until now.” (Mosiah 7:18-20).
“For behold, the Lord hath said: I will not succor my people in the day of their transgression; but I will hedge up their ways that they prosper not; and their doings shall be as a stumbling block before them… But if ye will turn to the Lord with full purpose of heart, and put your trust in him, and serve him with all diligence of mind, if ye do this, he will, according to his own will and pleasure, deliver you out of bondage.” (Mosiah 7:29, 33)
Ammon takes the opportunity to teach the people the things which were taught by King Benjamin, then Limhi brings forth a set of plates upon which are writings which no one in the kingdom can decipher. Limhi explains that a group that he sent out to find Zarahemla found the ruins of a great civilization, who they assumed had been the rest of the Nephites, and a set of records. Ammon says that he does not have the power to translate, but that king Mosiah has such power, that he is a seer, which, “is greater than a prophet… a seer is a revelator and a prophet also; and a gift which is greater can no man have, except he should posses the power of God, which no man can; yet a man may have great power given him from God” (Mosiah 8:15-16).
Then, after telling them this, we are given the record of Zeniff, which has been recorded on plates kept by the people of Limhi. The contents of these records are found in chapters 9 through 22 in the book of Mosiah.