The term "Christian" is a political term used to gather together people with fundamentally similar but inherently different beliefs to be united as a false unit to gain political power.
"A cult is just a religion that doesn't have political influence" - Unknown
The progression of the word "Christian" is amazingly interesting. The term "Christian" doesn't appear in popular culture until the late 1970's. An example of this: Every US President prior to this called themselves baptist, or protestant, or catholic, not "Christian".
Around 1980, some very clever people started being very inclusive when it came to religion, they bundled all those who believed in Jesus and the bible in a single group and called it "Christian". Individually baptists, or lutherans had a very limited political power, individually the bigger groups were only around 23%. When all these are brought together though, suddenly the number jumps to about 67%, making it much easier to legislate and fight things like abortion and gay marriage . It is also easier to win over a group of "Christians" (RE: government elections), rather than being specific and only gaining favor with your particular denomination.
I will now summarize some of the major denominations and their inherent beliefs.
Catholic - Generally more formal. Mass is weekly and is more ritualized. Priests wear more elaborate vestments. Priests take vows of celibacy. Catholics observe the seven sacraments. The pope is the lead guy, and most of the child abuse scandals are from this denomination.
Protestant - Contains a wide variety of denominations, some liberal, some conservative. Contains Anglicans, Lutherans, Baptists and Presbyterians, just to name a few.
Orthodox - There is less focus on the exact definition of religious truth and more on the practical and personal experience of truth. More metaphysical and spiritual than Catholic. Exact interpretation is not as important as personal truth. The "Holy spirit" is more of a big deal, and is worshiped more than in other denominations.
Anglican - The mid ground between Catholic and Protestant. The Church of England is Anglican. They are not subject to the Pope. Th are Protestant in most areas of doctrine, but retain many Catholic forms of worship. They have a hierarchy based on bishops, as in Catholicism. The Arch Bishop of Canterbury, goes in this group.
Baptist - Baptists have played a key role in encouraging religious freedom and separation of church and state. Martin Luther King was Baptist. Generally Evangelical in doctrine (take shit literally). Baptists generally oppose gambling, alcohol, tobacco. Believe that salvation is achieved through faith alone and not through works of our own. Strong emphasis on need for salvation (or you're going to hell).
Lutheran - Accepts the scriptures of the Old and New Testaments as the inspired Word of God. They Practice baptism (dunking you underwater and saying you're 'cleansed'). Widely varied beliefs about homosexuality within different Lutheran churches.
Everyone's beliefs very quite differently depending on which branch of "Christianity" they worship. For this reason it is important to distinguish what individuals actually believe, and not make assumptions, and not misuse statistics such as: 67% of people are christian, therefore at least that many oppose gay marriage.
The word "Christian" should be taken with a grain of salt. Answering "Christian" to "What religion are you?" is like answering "Human" to the question "what race are you". It's true, but doesn't convey much information.