"What are the similarities and differences between Christians and Muslims, Hindus, Mormons, Jehovah Witnesses, Jews, etc…???"
Christians, Muslims, Jews, Mormons (we could argue about this one), and Jehovah's Witness folk are all monotheistic (One God) faiths. Hindus are altogether different - polytheistic (many gods). The first three are closely related to one another while the later two split out of the Christian tradition.
The oldest is Judaism. Founded by God through Abraham when God asked him to leave his country and travel to another land that he did not know. Abraham and Sarah were old (70+) and childless when God told Abe that he would be the father of many nations.
Not believing God, Sarah and Abe took matters into their own hands and Sarah sent her servant in to sleep with Abraham. This produced a son named Ishmael. Sarah then got jealous of Ishmael and his mother (Hagar) and tossed them out. God miraculously saved them and founded the Arab peoples.
Judaism really has it's religious roots in the exodus from Egypt that happened several hundred years later. When God delivered his people from Egypt he set up a system of governance and religious belief that still exists today. Many of the ceremonies and rites that orthodox Jews observe today began there. The Scripture for Jews is basically what we would call the Old Testament.
A couple of thousand years later, Jesus was born, lived a perfect life, and died - only to be raised again to new life. This is the foundation of the Christian belief system - later expounded by Paul, Peter, John, and others. Jesus was a Jew, so Christianity is descended from Judaism. Most Christians accept the New and Old Testaments as Scripture - though some would add the Apocrypha.
Shortly after the time of Christ, a man named Mohamed (prophet according to Muslims) was born, met with Angels, and had several prophetic visions. He transcribed these visions verbatim - this is the Koran, which along with the Old testament - is considered to be the Muslim Scripture. Since Christians and Muslims share the Old Testament and are both monotheistic - many consider them to be "cousins".
Most of the trouble that has arisen between the three groups has taken place because of various interpretors of the scriptures in the intervening centuries. The Jews early campaigns against the Christians, the Christian's retaliatory attacks against Jerusalem, and the Crusades back and forth between the Christians and Muslims have all been devastating to these three major and related religious belief systems.
Many of our Scriptures are similar, but the way we interpret them is quite different.