Small question for a subject at least as big as the known Universe.
Mormonism, according to Brigham Young (successor of Joseph Smith), embraces all that is true, good, and holy. There is not a particle of truth, be it religious, philosophical, scientific, or historical, but what Mormonism claims and finds a place for in the great whole of all that which is, was, and will yet be. The greatest of these truths deal with the reality, identity, character, and plan of the great Creator, and our relationship to Him. It is these religious truths, and Mormons' often-unique view of them, that most people have in mind when speaking of "Mormonism." Mormons themselves, however, prefer to use the term "the restored gospel of Jesus Christ" to describe their religion.
It is so panoramic in its scope and intricate in its detail that it is understandable when newcomers sometimes have a hard time wrapping their minds around it all. It's not meant to be understood in one gulp. Grace for grace, line upon line, precept by precept: that is how we "grow unto the measure of the stature of the fulness of Christ" (Ephesians 4:13).
I find it helpful to consider the various doctrines to be sorted from the core to the peripheral. The core doctrine of Christ, as set forth by Himself, is simple and indispensable to our salvation. It is that if we have faith in Him, repent, and receive the baptisms of water and Spirit, we shall be saved by His grace; else we are damned.
That is the Doctrine with a capital D. There are, in addition to this core Doctrine, ancillary doctrines or eternal truths that help us understand in Whom we must have faith, what exactly we need to repent of, the meaning and mode of baptism(s), and what comes after we enter into the path leading to eternal life.
Beyond these are the doctrines of the gospel, which answer the grand questions of our existence and the sweeping plan of our Father. These put the Doctrine and its auxiliary doctrines into context. Nevertheless, the main message is Christ's Atonement; everything must tie back to that or be found useless.
And so here is a small sampling of the things Mormons believe:
* We are eternal beings; God is not only the Architect of the physical universe but the Father of our spirits. Of all that may be said about who and what you are, the truest statement of identity is that you are a child of God.
* Jesus Christ, as the Lamb of God, took upon Himself our sins and failings and weaknesses, and our sicknesses and victimizations and inequities. We need only accept His sacrifice and receive His ordinances and try our best to live by a certain defined set of laws, and He will take care of all the rest.
* God makes and keeps promises. He binds Himself to give generously as we make a good faith effort to hold up our end of the bargain. He delights in blessing those who honor Him, and is aggrieved mostly, if not solely, by our ingratitude of the mercies shown by Jesus Christ.
* Jesus Christ is the Only Begotten and Most Beloved Son of God. So trusted and loved by the Father is He that into His pierced hands the entire execution of the plan has been placed. He was the Lord Jehovah of the Old Testament, and the crucified Savior of the New. Father and Son (and Holy Ghost) are separate and distinct persons, united in mind and purpose. The Son can speak for the Father, and the Holy Ghost testifies of both Father and Son.
* Priesthood authority is necessary to the operations of the Church, and has been bestowed by angelic ordination of mortal men (Joseph Smith and his associate, Oliver Cowdery). All priesthood in the Church is traceable in a direct path to this ordination.
* There are a multitude of kingdoms and glories available, according to our response to His invitation.
* Families can be made eternal through sacred ordinances available in temples. This is not only a nice option, but is a vital part of His plan. The earth was created specifically so that our spirits could obtain bodies and that these embodied spirits (or "souls") could be welded together in a great family chain.
* God speaks to prophets today as in olden times. Not only that, but God answers the sincere prayer of faith without regard to eloquence or position. We may speak to Him, and He will speak to us. His answers guide our lives, but do not exceed the scope of our stewardship.
* The canon of scripture is not closed. He speaks to all nations, commands all to write what He speaks, and brings forth more or less of His word from generation to generation according as they have need and the faith to receive it.
* Jesus Christ will return to reign in glory upon the earth long before The Church of Jesus Christ of Latter-day Saints follows that well-worn path of apostasy followed by previous dispensations. Indeed, the Church is the stone seen by Daniel, the kingdom of God established in the last days and growing until it has filled the earth. It will never again be taken from the earth or allowed to fall into disrepair and corruption.
* Israel will be gathered and God's covenant with them fulfilled. The Book of Mormon, whatever else it may be (and that is much), is the great sign and the primary tool of that gathering.
* The American continent has played, and will yet play, a pivotal role in God's plan for this world. Nations that inhabit this "promised land" must serve the God of this land, which is Jesus Christ. If they do not so, but rebel until they are fully ripe, they will be swept off as has happened previously. The Book of Mormon tells of two such calamities and begs us to be wiser.
That's enough for now. Like I said, there is a whole lot here to learn and explore; this list barely scratches the surface. I am continually learning new things, and internalizing in new ways the things I already knew. It will be a long time, said the Prophet Joseph (paraphrasing), after you pass through the veil before you learn all there is to know about your salvation.