When compared to the beliefs of orthodox Christians, Mormons have a lot of weird beliefs about God: who God is, what God does, and what God wants. Mormons insist that the LDS Church is a Christian church and that they worship "God" just like other Christians. When you look at what Mormons believe about God, though, there are a lot of differences from traditional, orthodox Christianity. It's not hard to see why Christians and even non-Christians regard those beliefs as weird.
According to Mormon teachings, God was at one time a mortal human man, just like mortal human men on earth today. God was born, grew up, and lived on another planet and worshipped his own god — a god which instructed him in what humans know today as Mormon theology. God is thus essentially the same as human beings, but has progressed further along a spiritual path. In fact, it's a path that humans can also follow, eventually becoming gods themselves.
According to Mormonism, God is a physical, corporeal creature of "flesh and bone," not some sort of spiritual being like he might be described in traditional, orthodox Christianity. Mormons believe that God was once a human being and his resurrection was physical, thus he continues to have a physical body. Also, the idea that we humans were created in God's image entails that God must be both physical (since we are) and human (like us).
Mormonism teaches that God lives on a planet named Kolob or on a planet near a star named Kolob. Since God is a physical, corporeal being then it only makes sense that God would have to have a physical location or home somewhere in the universe. Mormon doctrine apparently knows just where that is, even though the location of "Kolob" cannot be verified by science and astronomy today.
According to Mormon teachings, God must be married. In fact, God might even have multiple wives. Mormon scripture doesn't specifically mention any wife or wives of God, but it's a belief that follows from a number of Mormon doctrines. That's why most Mormon leaders have taught and believed it as truth. The reason why God might be polygamous is because God once taught humans that they should be polygamous and the reasons for this would presumably apply to God as well. Just because God had to retract his teaching to appease the U.S. government doesn't mean he would have had to change his own marital status.
Traditional, orthodox Christianity teaches that God created the universe, but Mormon doctrine teaches that God is a part of the universe. According to Mormonism, the universe is eternal and filled with eternal truths, matter, intelligence, laws, etc. God was created out of this by another god and then created us out of the same substances. None of the basic material, however, was created by any of the gods, including the god worshipped by Mormons as God.
The Trinity is one of the defining beliefs of traditional, orthodox Christianity but it's explicitly rejected by Mormonism. According to Mormon doctrine, God, Jesus, and the Holy Spirit are not three persons in one, they are three entirely separate persons without any sort of unity. This follows closely the Mormon belief that there are many (perhaps an infinite number of) gods throughout the universe.
Whereas orthodox Christianity teaches that there is just one god, whom Christians simply call "God," Mormonism teaches that there are many worlds throughout the universe, each populated by human beings and each ruled over by its own god. The "God" of Mormonism and Christianity is thus just one of many and, like all the others, was itself a human being who has progress spiritually to the point where it can be entrusted with a planet of people to guide.
According to Mormon doctrine, God didn't stop instructing and teaching humanity with the texts collected in the Bible. Instead, God continues to reveal new information, teachings, and ideas to humanity. Sometimes, those revelations contradict and thus supersede past revelations. In this way, Mormons believe that they have received revelations which supersede biblical revelations and that, in turn, is the basis for the many contradictions between Mormon beliefs and practices and traditional Christian beliefs and practices.