The four Gospels tell of the birth, life, ministry, teachings, death and resurrection of Jesus. The Gospel of Mark was written around 70 A.D., about 40 years after Jesus was crucified. Matthew and Luke were written between 80 and 90 A.D. Finally, the Gospel of John appeared in its final form around 95 A.D.
Matthew, Mark and Luke (the "synnoptic gospes") are very similar. It is commonly believed that Matthew and Luke incorporated much of the material in Mark and another common source that is now lost. Each author then added some unique material.
The Gospel of John is quite different. It is much more of a spiritual and theological work, although it relates many of the same events as the other three Gospels.