What do Christians believe?
There are two important parts to Christian belief. Firstly, Christians believe in a God who is an all-powerful intelligent being, existing independently of the physical Universe, and responsible for its creation. We also believe that God cares deeply about the Universe and all of its inhabitants.
This belief is common to many major religions. Jews, Muslims and Christians all worship the same God, in different ways.
Secondly, Christians believe that Jesus of Nazareth (c. 6 BC to AD 27) was a manifestation of God on Earth as a human, and that His teaching as recorded in the Bible is therefore a direct insight into God's wishes for humanity.
Lots of people have claimed to be gods. Why do Christians believe Jesus really was?
There are several good reasons. Firstly, He taught a path of self-denial and caring for others, and followed these teachings Himself, and as a result He was executed by the Romans. This is hardly the behaviour you'd expect from a person claiming to be the Ruler of the Universe—unless He was telling the truth.
Secondly, He was clearly not a construct of people's expectations. The Jewish people of the time had prophecies concerning a Messiah, but they were expecting an Earthly ruler—although with God's authority—who would kick out the Romans and make Israel great again. Jesus was not at all what they had expected. Later theologians had great difficulty in finding Old Testament 'prophecies' which actually seemed relevant. And yet—without once commanding an army or possessing any material wealth—Jesus became the most influential person in recorded history.
Finally, Jesus rose from the dead shortly after His execution, and appeared to hundreds of his followers before (we assume) returning to God. Whether you believe this or not depends on how much weight you give to these eyewitness accounts, and to the simple fact of Jesus' continuing, dramatic influence on history through the people who had known him.
So what did Jesus teach?
Jesus came not to form a new religion, but to reinforce and improve people's existing relationships with God. His main commandments were to worship God, and to care for other people. He said that God has very high standards—but that God understands that we usually can't live up to them, and loves us nonetheless. God is always willing to forgive, and let us make a clean start, as long as we keep trying.
The very presence of Jesus shows that the God who created the universe, and who probably knows the position and state of every subatomic particle, also cares deeply about individual humans, and wants us to love Him and live fulfilling lives in accordance with good moral principles.
Christians believe that when Jesus became human, He opened the door for us to become more closely connected with God. He revealed to us a God who wants to be in close personal relationship with everyone—including YOU!
Where does the Bible come in?
The Bible is the record of humanity's gradually increasing knowledge of God, culminating in the Gospels—four accounts by different writers of the life of Jesus. It is humanity reflecting on its experience of God.
Is every word of the Bible true? Do Christians believe that the Earth was created in seven days?
Some do, but this is not a common view in mainstream churches. Christians believe that the Bible was inspired by God. However, different parts of it were written for different audiences and not all of it is intended as literal history. Christians take the teachings of Jesus, as recorded in the Gospels, very seriously indeed.
Is Christianity incompatible with science?
No. It can't be, because science is a self-correcting method of finding truths about the Universe, and we believe that Christianity is one of these truths. As a general principle, science tells us 'what' and 'how' and religion tells us 'why'.
What about life after death?
Christians believe that human consciousness doesn't cease when we die. We don't know what Heaven is actually like; it's probably something well beyond our current capacity for understanding. We believe that we will have a permanent existence in the presence of God, in a form fuller and richer than our current physical one.
What is the Trinity?
The short answer is; we don't know. Christians see God as having three aspects; God the creator, Jesus of Nazareth, and the Holy Spirit, which is the manifestation of God which we believe can still interact directly with human beings. We do not believe that God is a sort of committee; the idea is more that a single God appears in different forms for different purposes. In the past, theologians have attempted to explain and codify the idea of the Trinity, but in fact it's something which we don't fully understand.