The Mormon Handbook is a reference to The Church of Jesus Christ of Latter-day Saints (LDS), headquartered in Salt Lake City, Utah. It is not to be confused with the LDS Church Handbook of Instructions.
After the death of Joseph Smith, the church he founded split into several organizations. Those who sided with Brigham Young followed him to the Salt Lake basin in Utah, where today the LDS church is the largest of those who still regard Joseph a true prophet.
Members are called "Latter-day Saints" (LDS) or "Mormons", after the Book of Mormon, which purports to be "another testament of Jesus Christ". LDS and Mormon are used interchangeably throughout the handbook.
The Mormon church claims to be the only true Christian church today. Mormons believe that the original church founded by Jesus Christ went into apostasy soon after his apostles died, and was restored in 1830 by their prophet Joseph Smith. Mormons believe that the Bible and true doctrine were corrupted during this span, and believe that today's LDS church is nearly identical to the original church.
Because the Mormon church claims to be the only true Christian church, the handbook presents a comparison between Mormonism and Christianity.