Christianity began with Christ. I know that sounds simplistic, but in fact, that is the beginning. Jewish followers of Christ were the founders of the Christian religion about 2000 years ago in Israel.
At the time of Jesus, the Jews in Judea were under Roman rule. The Romans for the most part, were pagans which was very intrusive on the Jewish way of life. Some Jews chose to conform to the Romans ways while others became religious zealots, resisting Roman rule. Still others withdrew themselves and waited for the coming of the promised Messiah. When Jesus arrived on the scene, many of his followers believed he was the one to lead them against Rome.
Although Jesus observed the Jewish faith and was well acquainted with Jewish law, his teaching was contrary to the religious leaders’ doctrines and tenets and was revolutionary. It challenged the established religious authorities to repent from their self-righteousness and hypocrisy and realize that the Kingdom of God is rooted in service and love.
Jesus' teachings created problems for the Jewish authorities since so many people were embracing it. He began his teaching with the disciples who he taught about the will of God and about the "new covenant" God was bringing to humanity through Him. Jesus showed them that mankind were sinners and did not have a relationship with God. He revealed to them that the purpose of this "new covenant" was to restore those who accepted it, into a renewed fellowship of forgiveness and love with God.
He taught that the remission of sin was accomplished through the sacrifice of a spotless lamb and he was that lamb and would pay for the sins of all humanity by being crucified unjustly on a Roman cross. He also taught that he would rise to life after three days to give hope to a hopeless world.
Most of the historical records for the start of the Christian faith can be found in the New Testament. But, the history of Christianity actually began with prophecy in the Old Testament with over 300 predictions that span over 1000 years throughout the Old Testament concerning the coming of a Jewish Messiah.
If you study Jesus' life, death and background, it will show that He fulfilled the Messianic prophecies. In fact, you can see Jesus throughout the entire Passover Seder, the yearly celebration of the liberation of the Jews from Egyptian rule of 400 years.
Jesus taught that he and God (the Father) were one and that he was going to send the Holy Spirit to lead and guide the people once he left. Those are the three elements of the Trinity although the word trinity is not in the bible.

There is no exact date as to the origins of the Christian religion. Here is a resource which can give an overview of how the religion started and spread throughout empires. Hope it helps.

Source : http://www.whenguide.com/when-did-christianity-start.html