Since Christianity and Judaism share the same history up to the time of Jesus, they are very similar in many of their core beliefs. There are two primary differences. One is that Christians believe in original sin and that Jesus died in mankind's place to save mankind from that sin. The other is that Jesus was the Son of God and part of the Holy Trinity: God the Father, His Son, and the Holy Spirit. All Christians believe in heaven and that those who sincerely repent their sins before God will be saved and join Him in heaven. Belief in hell and satan varies among groups and individuals.
There are a multitude of forms of Christianity which have developed either because of disagreements on dogma, adaptation to different cultures, or simply personal taste. For this reason there can be a great difference between the various forms of Christianity they may seem like different religions to some people.