According to biblical scholars and archaeologists, the Gospel of Mark originally ended with the resurrection of Christ. Mary Magdalene, Mary the mother of James, and Salome went to the tomb of Jesus and found it empty. Instead of the body of Christ, they found a man or angel (depending on the translation you use) inside the tomb who told them,
You are looking for Jesus the Nazarene, who was crucified. He has risen! He is not here. (Mark 16:6)
The women were "bewildered" and fled. That was the end of the Gospel.
Mark is presumed to be the first gospel that was actually written. However, early Christians viewed the account as somewhat insufficient compared to the other three gospels, which provide an account of Christ appearing to followers after his death, among other details.
Somewhere in the early days of the New Testament, editors added verses 9–20. These verses focus on the appearances of Christ to various believers following his resurrection.
First, Jesus appeared to Mary Magdalene, and she left to tell mourners of her experience. At first, they didn't believe her. Then Jesus appeared to mourners who were out talking. They also returned to share the news with others, but no one believed them, either. He then appeared to his eleven remaining disciples and admonished them for their lack of faith in believing the witnesses who attested to his resurrection.
Christ then commanded the disciples to go into the world and preach the Gospel everywhere. He told them to baptize all those who believe in Him. After Christ finished speaking with the disciples, he ascended into Heaven to sit at the right hand of God, and His disciples obeyed his commands, sharing their faith and experience everywhere they traveled.