The Tomb
Mark 16:1-8 records the activity of the women who came to take care of Jesus body. It was customary to anoint the bodies of the dead with spices as a matter of respect. Little did they understand that when the woman broke the spikenard over Jesus head and Jesus said she was anointing Him for burial, that that was truth and not an expression. Because, hallelujah, He was risen. We don't know exactly when it happened, but I suspect as soon as the three days were up to fulfill prophecy, Jesus was out of there. All we know for sure is that when the women came at the rising of the sun, the stone was rolled away, Jesus body was gone, the guards were gone, and there was an angel sitting by where His body had lain.
This angel spoke truth to them as well, and also encouragement. The angel, of course, knew who they were seeking. His simple statement was to not be afraid, but that Jesus who had been crucified was risen and that He was on His way to Galilee and for Peter and the disciples to go and meet Him there. All had happened just as Jesus had foretold. In spite of the angel's encouragement to not be afraid, it didn't work and they fled with fear in their hearts, and were afraid to tell anyone about what they had seen.
The Promise
Mark 16:9-14 doesn't record many of Jesus interactions with people after He arose. Mary Magdalene is mentioned and she went and told the disciples that she had seen Him, but they didn't believe her testimony. Times haven't changed much I guess. It is still hard for people to believe first that God would come and live as man and allow Himself to be crucified, or that a man who was crucified could be resurrected and live again. The Bible tells of Lazarus. It tells of Jonah. It tells of others who came back to life after shorter times. But even those closest to Jesus who had been told by Him that He would die and rise again, couldn't believe. Grief can really mess with your mind.
Then the two who had talked with Jesus as He walked with them came and testified, and they didn't believe him either. Finally, he came to the eleven remaining disciples as they were eating and upbraided them for their unbelief and hardness of hearts because they didn't believe the testimonies they had heard. How blessed we are who believe without having seen Christ walking the earth. How ashamed many in Israel must have been who had seen His ministry and heard His teaching and turned away from Him at His death or even before, never to return.
The Commission
At that point, Mark records what has come to be known as the Great Commission (Mark 16:15-20). The disciples, and by extension, the rest of us, are called to go into all the world and preach the gospel to every creature. For those who believe and are baptized will have eternal salvation. Those who reject Christ will be damned.
He also promises that the gifts of the Spirit will be poured out on the believers. He mentions speaking in tongues, and healing specifically. He also promises power over Satan's realm for Spirit filled believers. After He had uttered His commission, He went back to Heaven and the end of Mark records what was essentially a summary of Acts and beyond that the disciples did that. And what Jesus had said was true. The Lord worked with them and works followed the believers.