Gospel of Mark
The Gospel of Mark is the second gospel of the New Testament; considered by most scholars to be the first gospel written. Like the other four gospels; Mark (known as John Mark) was one of the 12 disciples who used Peter as the primary source of his gospel as well as his own personal experiences.
Most modern scholars date this gospel to around 70 AD a time of great peril of the church, when the temple was destroyed in Jerusalem; the city where the community first started off. It was written mainly for a Gentile audience as evidence can be seen for the lack of Jewish customs (7:3-11.) and it’s concentration of Jesus as hero an action man, exorcist, healer and miracle worker. 
Mark is most brief of the gospels which centers around the main them of Jesus Christ as the Servant and Sacrifice.
The Suffering of the Messiah (8:27-33) Being rejected by the elders and chief priests and the passion of Jesus Christ [crucifixion.] This suffering was analogous for his immediate disciples who say as their Messiah tribulations. The Messianic Secret (1:34, 44; 8:30) One of the main reasons he wanted to be secret was to avoid public attention of the Romans and Jewish religious authorities such as the Sanhedrin (via Saducee and Pharisee agents) who saw him as a threat. Later in the New Testament, Paul in his writings, used this description of Jesus because we are lost without him if we are in the world (non-Christian.) Discipleship (8:34-38) Only the gospel saves and will be with you forever. Invitation to be in the presence of God and the holy angels.
Outline Prologue: Preparation for the Ministry (1:1–13) The Galilean Ministry: The Kingdom Is at Hand (1:14–6:29) Jesus manifests the power of the kingdom (1:14–45) Israel is divided over Jesus’ authority (2:1–5:43) Nazareth divided: doubters and disciples (6:1–13) The Forerunner beheaded (6:14–29) Ministry Beyond Galilee: The Kingdom and the World (6:30–9:50) Jesus relates to the Jews (6:30–7:23) Jesus relates to the Gentiles (7:24–8:26) The glory of the kingdom revealed (8:27–9:13) The response of this world (9:14–50) Journey to Jerusalem: The Kingdom's Discipline (10:1–52) Ministry in Jerusalem: Rejection, Persecution (11:1–16:20) The Messiah made manifest (11:1–13:37) Betrayal and Passover meal (14:1–31) The Passion (14:32–15:47) The Resurrection (16:1–20) See under main entry Jesus Christ which discusses these themes in more details.
Early minority manuscripts end the gospel at Mark 16:8, however Majority Manuscripts (Byzantine) has 12 more verses and so therefore ends at verse 20. Early tradition suggests the longer ending to be valid and therefore historical because early Church Fathers such as Ireneaus quote from these verses. There is one manuscript called the Freer Logion manuscript (dated fourth-fifth century) which says “And they reported all the instructions briefly to Peter’s companions. Afterwards Jesus himself, through them, sent forth from east to west the scared and imperishable proclamation of eternal salvation amen.” Although this is not considered canonical, it maybe an early Christian tradition of how the author first assembled his companions into preaching. This hints of the authorship of Mark via Peter due to him giving out the commandments of his disciples.
Orthodox Study Bible, Wikipedia, New American Bible