What are Major Christian Beliefs?

Christianity is at least three things:
A set of beliefs
A way of life
A community of people
Different Christian groups place different weights on these three aspects, but they always involve all three. All three aspects are based on the life and teachings of Jesus of Nazareth, who is also known as the Christ. ("Christ" was originally a title. It is the Greek form of the Hebrew "Messiah", meaning "anointed".)
This page is an introduction to the beliefs. To get a reasonable picture of Christian beliefs, you should read at least this page and the next one, on the Gospe. In case you are interested in more details, there are also several pages dealing with specific beliefs: the Incarnation, the Trinity, and a set of issues involving free will and God's overall responsibility. The latter page is called predestination.
For the role of the Christian community, see the page on the church. For the way of life, see the pages on the Christian life, worship, the law, and expressing love.
Christianity shares a number of beliefs and practices with other religions, particularly Judaism and Islam. With Judaism and Islam, Christians believe in one God, who created the universe and all that is in it. All believe that this God is active in history, guiding and teaching his people. All three religions, including Christianity, have been called "ethical monotheism". This term emphasizes the belief in one God, and the fact that following this God commits us to a number of specific ethical rules or principles.
Christianity originally developed as a part of Judaism. Jesus was a Jew. He lived from about 3 BC to 30 AD. He lived and taught in Palestine, primarily (although not exclusively) among fellow Jews. Christianity separated from the main body of Judaism for two major reasons:
Christianity came to regard Jesus as in some sense God's presence in human form. This was unacceptable to most Jews.
Judaism is defined by a covenant made between God and the Jewish people. Part of this covenant is the Law, a set of religious and ethical rules and principles. Most Christians came to regard both this covenant and Law as in some sense superseded by Jesus' teaching and the community that he established. On the night he died, Jesus talked about establishing a "new covenant" based on his death and resurrection.
These two issues continue to be among the most distinctive and controversial aspects of Christianity. They are controversial even among Christians. All Christians assign Jesus a role that would seem inappropriate to Jews. However his exact relationship with God was the source of major disagreements among Christians as late as the 5th Century. While most modern Christians accept the standards developed in the 4th and 5th Centuries, there are small groups that do not. This aspect of Christianity is also often attacked or reinterpreted by "liberal" elements within Christianity.
The role of the Law also continues to cause controversy within Christianity. In a narrow sense this is reflected in small groups of Christians that worship on Saturday rather than Sunday, in obedience to one of the provisions of the Law. In a broader sense, the current conflict about the role of women and homosexuals in the Church involves the Christian approach to ethical and cultic standards.