(the following is partly a respones to a question i asked, but also a respones to this video.)

Mormons believe that we are all literal children of God. Before we were born on Earth, we lived in heaven with God, who we frequently refer to as "Heavenly Father". Before the world was created, God assembled all of his children and set out to create a plan, Christ presented one plan, Satan presented another.

Christ wanted to allow humans to have free agency and to come to earth and to worship as they chose, but be responsible for the consequences, Christ said that the glory for this plan would be the Father's.

Satan wanted all men to be forced to do the bidding of God, but wanted the glory and the power to be given to himself, thus making humans nothing but mindless drones, controlled by him.

God chose the plan of Christ, and Satan got pissed and rebelled and was cast out, taking with him 1/3rd of all the spirits who followed him instead of Christ.

The rest of the spirits followed Christ. Those who did this are all the human beings that have lived, live, or will live on earth. Mormons believe that everyone, no matter how bad they are in their lives, originally accepted Christ's plan in the "preexistence". Those who didn't accept those plans are the angels of Satan, whether or not some say these are the generic interpretation of what demons are, that's up to individual interpretation.

Anywho, Mormons believe that God created the earth, through Jesus, and that many spirits participated in the creation of the earth. The original Hebrew version of the old testament actually says "in the beginning, the gods created the heavens and the earth". Mormons believe in the Bible, but certain areas are interpreted a bit differently.

Now, Mormons don't worship gods, they worship only one God. The two meanings are very different in the original Hebrew translation. God, with a capital G when translated into English comes from the word "Elohim" which refers to a "Supreme Being", that is what Mormons refer to as Heavenly father. But "god" with a lowercase g was translated from a word which simple meant "heavenly being". Now, God has a son, Jesus Christ, and a helper... the Holy Spirit. Mormons believe in the trinity, except the difference is Mormons believe that the Father and Christ are both two distinctly different human beings, yet immortal and perfected. Along with the Holy Spirit, they make up the Godhead, which acts with one purpose, but is not one singular, one God, being as many Christians interpret.

Now, the issue about Mormons believing that God came down and had sex with Mary is a COMPLETE LIE. Mormons don't believe that. Although they believe that God has a body, Mormons believe that Mary conceived Jesus by the power of the holy spirit, not by physical, sexual intercourse. Mormons DO believe in immaculate conception.

So basically, Mormons believe in the Bible, mostly identically to the way Christians do. But a bit differently, with a bit more doctrine concerning what happened prior to genesis.

However, Mormons also believe that shortly after the crucifixion of Christ, Christianity became apostate and the churches that made up Christendom for the next several centuries were false, and were tainted by worldly teachings and had lost the original, correct interpretations.

Now, Mormons believe that just like how throughout the history of God's interaction with humans in the middle east is documented in the Bible, they believe that God also interacted with people who lived in the Americas. The record that the inhabitants of the Americans kept (assuming just for the sake of argument that the story is not a lie) is referred to as the Book of Mormon, a Bible-like collection of books from a few civilizations, telling the story of what supposedly happened.

Now, Mormons believe that since Christianity was in apostasy, God had to provide new revelation to humans. Just like he did in the Bible, Mormons believe that God called a prophet to deliver his message to the world. Mormons believe that Joseph Smith was called by God to deliver the account the Book of Mormon to the world, and to create a new true church based on the augmentation of new revelation.

This is where it gets wacky, yes, Mormons believe that an angel named Moroni appeared to Joseph Smith and told him to find golden plates, on which the Book of Mormon was written and deposited almost about 1600 years ago by the last of the prophets who were killed off in the Americas. Mormons believe that Joseph Smith was tasked with translating it and using its contents, in addition to the doctrine of the Bible, to establish a new and living church of God, as the restoration of what was once the complete knowledge that the true church had 2000 years ago.

Now, that's the back story.

As for what Mormons believe about heaven and everything:

Mormons believe that in order to receive salvation, all men must receive atonement through Christ, repent for their sins. However, Mormons don't believe that people who don't do this during life go to hell. The belief is that people also have a chance to learn about and receive Christ after death, and that all those who eventually accept Christ are spared from a spiritual death.

Now, as Children of God, Mormons believe that those who are truly righteous and receive God in the fullest become heirs of God, becoming similar in power to Christ. Now, little do Christians realize, but this is actually a Biblical belief:

Romans 8:16-17

The Spirit itself beareth witness with our spirit, that we are the children of God:

And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.

So, basically the main idea behind Mormonism is that the purpose of life is to progress, and that God's plan is one that leads to humans receiving salvation and to eventually come back in to the presence of God, and to eventually become not equal to, but similar to Christ.