The various differences between Christians and LDS or Latter-Day Saints stem from the fact that LDS also has a separate scripture it uses together with the Holy Bible, and also differs from other denominations in Christianity when you consider their understanding of some parts of the Bible. This scripture is called the book of Mormon.
Although Latter-Day Saints tend to see themselves as Christians, the real Christians don't see them as one because their beliefs and understanding about some things in the Bible are not the same. For instance, while Christians usually think of God as a divine being or spirit, Mormons or Latter-Day Saints see God the father as a being with the physical body, meaning God has bone and flesh.
Another difference in their understanding of the Holy Bible is the belief that humans are not supposed to share in the sin that came through Adam, whereas Christians believe all men, before accepting Jesus Christ, are sinners because it came from the first man as revealed in Romans 5.