One of the most common questions I get from fellow Christians is what really distinguishes The Church of Jesus Christ of Latter-Day Saints from other Christ-based religions; essentially, what makes Mormons different? Despite the many similarities between the LDS church and other Christian religions: belief in God, belief in Christ as our Savior, belief in the Bible as the word of God, etc., there are some important differences. Here are, arguably, the two most important:
1. Mormons believe in present-day revelation.
Similar to prophets from the Old Testament such as Moses, Samuel, Isaiah, and others, Mormons believe that God has called a prophet to guide His church in these days. This prophet (Thomas S. Monson), who also presides over the church, fulfills the same role as prophets do in the Old Testament: he testifies of Christ as our Redeemer and guides and directs Christ's church through revelation, helping us know how God wants us to live as we face contemporary challenges. Because we believe that the Church of Jesus Christ of Latter-Day Saints is Christ's church that he organized while on the earth, we also have twelve apostles. These apostles fulfill the same role as those Christ called when he was on the earth: they testify of Christ and lead and direct his church. Mormons believe that Joseph Smith was called to be a prophet to restore the church Christ organized when He was on the earth, with the same structure--prophets and apostles--He instituted.
2. Mormons believe The Book of Mormon is God's word.
The Book of Mormon is actually where we get the name, "Mormons." We consider the Bible God's word and a testament of Jesus Christ. Similarly, The Book of Mormon is another testament of Jesus Christ. Because God loves all His children, Mormons believe that God calls prophets to teach people about Christ among all believing peoples; He wants all of His children to learn about Christ's grace. The Book of Mormon chronicles the teachings of prophets among a group of ancient Israelites who traveled to the Americas 600 years before Christ's birth. Mormons see The Book of Mormon as scripture because it is written by the prophets who taught this group of ancient Americans about Christ, His birth, crucifixion, and eventual resurrection. The culminating moment in The Book of Mormon is when the resurrected Christ comes and visits His people in the America's and establishes His church after He leaves His twelve apostles in Jerusalem.
If you have a question about what Mormons believe, feel free to ask. I'll do my best to clear up any misconceptions and answer your questions as best I can.