Ok here are some
major differences between LDS and Christians. Much can be found at
http://www.carm.org/mormon.htm, http://www.carm.org/lds/lds_doctrines.htm,
Jesus and Satan are spirit brothers and we were all born as siblings in heaven to them both, (Mormon Doctrine, p. 163.)
There is no salvation without accepting Joseph Smith as a prophet of God, (Doctrines of Salvation, Vol. 1, p. 188.)
A plan of salvation was needed for the people of earth so Jesus offered a plan to the Father and Satan offered a plan to the father but Jesus' plan was accepted. In effect the Devil wanted to be the Savior of all Mankind and to "deny men their agency and to dethrone god." (Mormon Doctrine, page 193; Journal of Discourses, vol. 6, page 8.)
God used to be a man on another planet, Mormon Doctrine, p. 321. Joseph Smith, Times and Seasons, Vol 5, pp. 613-614; Orson Pratt, Journal of Discourses, Vol 2, p. 345, Brigham Young, Journal of Discourses, vol. 7, p. 333.)
God the Father had a Father, (Joseph Smith, History of the Church, vol. 6, p. 476; Heber C. Kimball, Journal of Discourses, vol. 5, p. 19; Milton Hunter, First Council of the Seventy, Gospel through the Ages, p. 104-105.)
God had sexual relations with Mary to make the body of Jesus, (Brigham Young, Journal of Discourses, Vol. 4, p. 218, 1857; vol. 8, p. 115.) - This one is disputed among many Mormons and not always 'officially' taught and believed. Nevertheless, Young, the 2nd prophet of the Mormon church taught it.
God is married to his goddess wife and has spirit children, (Mormon Doctrine p. 516.)
The trinity is three separate Gods: The Father, the Son, and the Holy Ghost. "That these three are separate individuals, physically distinct from each other, is demonstrated by the accepted records of divine dealings with man." (Articles of Faith, by James Talmage, p. 35.)
If it had not been for Joseph Smith and the restoration, there would be no salvation. There is no salvation [the context is the full gospel including exaltation to Godhood] outside the church of Jesus Christ of Latter-day Saints, (Mormon Doctrine, p. 670.)