I've realized more and more now that people who believe in that church aren't all exactly like I was, in that they don't all hold the same teachings as authoritive as I did... I accepted their prophets' words as truth and inspired in everything, while others don't. I accepted past leaders' words as scripture as well, while others don't really care as much about that. Individuals sometimes have very strong opinions that override existing doctrine, too, so it isn't as clean-cut as it may seem at first.
So while I, and those sites that others have recomended, can tell you the commonly held beliefs among LDS (Mormons), it is definitely a risk to go up to your friend and say "You believe that you can be a god if you're worthy and righteous and 'endure to the end.' " Is that taught? Yes. Is it in the lesson manuals? Yes. It's all available online at their official site, surprisingly. Does everyone embrace that teaching, or even know it? No.
Your thread referenced the Book of Mormon. Are you mostly just wondering what that's about? It's a book, about 530 pages long. It's divided into 15 "books" and into verses (like the Bible). It claims to be a written record of some groups of people who travelled from Jeruselem to the Americas as they were led by God to "the promised land" (America). There are sermons and at times, honestly, it can sound somewhat Biblical. It quotes Isaiah and I think even the Sermon on the Mount. It claims that Jesus Christ appeared to the people there after His resurrection.
There are some things in it that contradict the Bible, but not as much as some people think. The LDS church does have the BoM, but they also have other books they consider scripture, and that's where a lot of the unique beliefs come from. For example, the view of temples isn't mentioned in the BoM, yet temples are viewed as basically the most sacred places on Earth.
In the Doctrine and Covenants, there are sections (chapters), that describe their concept of a three-level Heaven, the requirements for those degrees of glory, guidelines for polygamy (which although not practised today by the LDS church, is still in their scriptures), and the "Word of Wisdom" which says not to drink "strong drinks" or use tobacco or even eat meat unless it's winter or famine (I've never heard of anyone who abstained from meat like that, but the no alcohol/tobacco rule determines who can attend a temple and other things). It's full of the deeper doctrines and stuff...
It also says that God the Father has a physical body like Jesus does, but that the Holy Ghost (Holy Spirit) does not. It's taught that they are three distinct indivudals and that Jesus is a spirit child of Heavenly Father (and later leaders have alluded to a Heavenly Mother).
The Pearl of Great Price claims to be a translation of some writings of Abraham found on some Egyptian papyri that was purchased by Joseph Smith's followers. There's also a book in there that Smith claimed was from Moses. From the Pearl of Great Price comes "scriptural support" for their belief in a pre-existance of all spirits and that the devil and angels are beings just like us (minus a mortal body) and that we (the "valiant spirits who chose to follow Jesus in the pre-existance instead of Satan) are all just trying to return to our Heavenly Father (very literally the father of our spirit bodies...), and it has a few Egyptian pictures/diagrams, too. The diagrams are not fully explained.
The importance of the BoM to LDS isn't necessarily in its pages. It's the story behind its origins, and belief in the truth of the BoM is the first thing the missionaries try to set up for potential converts. The potential convert is told that to know if the BoM is true, he or she only has to pray about the book and God will confirm its truth, usually with a warm, peaceful feeling.
See... Joseph Smith claimed that he was confused which Christian denomination to join. Then he claimed that he received a vision from God and Jesus (two seperate people simultaneously), and they told him not to join any, because they were all corrupt. And he said that 4 years ater that vision, he received the golden plates, a book made of thin metal sheets with a language he called "reformed Egyptian" written upon them. He claimed that's what the BoM was translated from, by the power of God. He claimed he was chosen by God to be the prophet who would usher in the restoration of the fullness of times, the last dispensation before the Second Coming of the Lord. Belief in the BoM as scripture from God means belief in Joseph Smith as a prophet, and in his authority and teachings.
Also, for modern-day Mormons, that line of authority is believed to have gone on after Smith's death to Brigham Young, then John Taylor, Wilford Woodruff, Lorenzo Snow, etc.... all the way to current day "prophet, seer, and revelator" Gordon B. Hinkley. So teachings of those men and other leaders (they have a quorum of twelve apostles and other groups under them, all the way down to the congregation level) are viewed as inspired.
How inspired those statements are considered varies from one LDS to another. I've talked with some who only accept their scriptures, and then there are people like me who hung on the prophets' every word whenever i could hear them speak...
Each "worthy" male is also ordained with the power of the priestood, ("authority to act in God's name") to heal, to bless, to prophesy, administer the sacrament (the Lord's Supper), baptize, etc. Women ask their husbands or other worthy priesthood holder for blessings.
My family tells me over and over again that they are Christians. I don't fight them over that. It wouldn't really help anything. When I was a Mormon, I viewed myself as Christian too. The same words can mean different things to different people, though.
In Mormonism, "salvation" is generally believed to mean life after death (resurrection), but exhaltation is the highest form of Heaven. So they will undoubtedly agree on Jesus being the only way to salvation, and that it's a free gift, but that's because they are just thinking of immortality.
"Heaven" can mean any of the three kingdoms of glory (telestial, terrestrial, celestial) or just the top one. Hell can be just "outer darkness" (where apostates and the most evil people go), or any kingdom of glory except for the celestial. Why? Because only the top, the celestial, is believed to allow eternal progression and eternal family and eternal offspring... godhood. Anything else is damnation for eternity in a sense.
Baptism into that organization is required. This is usually done at the age of 8, but all converts are required to be baptized.
Baptism is so important that members will go to temples to do baptisms for the deceased vicariously in order to give them the chance to also have exhaltation if they are judged worthy (baptism is required for the highest level of Heaven). Vicarious marriages (they have to be done under LDS authority to be valid for eternity) are also performed. That is a huge reason for the interest in geneology/family history among LDS. They need names in order to baptize and perform other ordinances for them.
Admittedly, I listed some differences, not similarities. There is common ground, especially among those individuals who may trust the Bible more than their leaders and "additional scripture." It seemed like you were wondering more about differences with your thread, though.
I also don't dare go into the works vs grace topic because individuals interpret it differently. I can't even figure out what my dad believes on that... I know what I was taught and what I believed, and even what's common, but it does vary. I did not appreciate the sacrifice of Jesus Christ as much as a Mormon, though. And the emphasis was always on teh garden of Gethsemane, not the cross. That's where I was taught the Atonement took place-- in the garden, not on the cross. The cross was just the end, and the garden was more painful. Mormons are discouraged from wearing crosses or using the symbol, and non eof their buildings have crosses on them. "If your brother had been killed by someone with a knife, would you wear a replica of a knife around your neck in remembrance of him?" is something I've heard in defense of that.
Also, I don't know what your friend personally believes in general. Depending on his age and experience, activity in the LDS church, outside reading/study he's done, he may know more or less about that church than I did at his age.
I think if you want to try to witness to your friend you're going to have to ask him lots of questions, and if you can, avoid telling him what he believes. That gets very frustrating when people tell you what you believe and put words into your mouth.
Just discuss, you know? Getting background info on the general beliefs of the people in the religion will help, but every person is very different.