Why are there so many Christian denominations?
Splintering within the faith community goes back to ancient times. Some of the divisions are based on fundamental differences, like the rural shrines that Israelites established after the wilderness wandering vs. the urban temple they built in Jerusalem, or temple cult vs. synagogue. These came about because people had different historical experiences, different views of the world from present reality (e.g. countryside vs. city), as well as the usual differences among people's perceptions and desires.
The Christian community splintered from the very start, with some following James and the Jerusalem church, some following Paul and his mission to the Gentiles, and some following other local leaders. Each of the four gospels was written for a different church, which explains why they are so different.
The Bishop of Rome tried to impose global order on Christianity, but that never happened. East and West divided early, outlying bishops vied with Rome for power, and eventually nationalistic movements began in England (Church of England), Germanic States (Lutheranism), Scotland (Presbyterianism), Switzerland (Calvinism), and elsewhere.
Those national churches eventually became separate denominations. When the American continent was colonized, those divisions came along and had a large influence on early colonial life. Even Roman Catholicism, supposedly monolithic, had different ethnic expressions in the US.
In the 19th century, American Protestantism divided further with the advent of revivals, Great Awakenings, evangelicalism, fundamentalism, Northern and Southern branches after the Civil War, black denominations like AME Zion, and, late in the 20th Century, the vast expansion of non-denominational congregations like Willow Creek and Saddleback.
To see what each stands for, I suggest you start with Wikipedia, an on-line encyclopedia. Eventually, you will need to experience them for yourself. Each denomination has some uniqueness, and within each denominations are further differences (like High Church and Low Church within Anglicanism).
In the end, as Rep. Tip O'Neill said about politics, all religion is “local.” You make your home in a specific faith community, join its mission work, love its people, learn from its pastor, and find God through its community life.