As the early church sought to understand what Jesus had said and been, they developed the understanding (doctrine) of the Trinity - often called from respect the Holy Trinity. Those beliefs are formulated in the creeds. The device to the right attempts, inadequately, to portray the concept of how God is One, but in three Persons

God the Son
2nd Person
Jesus - the Christ (the Messiah). Although Christians speak most of Christ's life on earth (around 0-33AD) he was not created. He was involved in creation and was the Human form that appeared to certain Old Testament prophets to bring God's word. In his death, he died for humankind. By his resurrection he demonstrated his divinity and his power to raise believers at the end of time.

God the Holy Spirit
3rd Person
The Spirit of God has also been present from the beginning. He was involved in creation and acted in many Old Testament situations. However, Jesus particularly promised his disciples that after his physical departure the Spirit of God would come upon them in power. This happened on the day of Pentecost. His Spirit remains with Jesus' followers today

Although the concept is difficult, it reflects the way in which Christians find that they understand God the Father through the reconciling work of Jesus and experience the power of the Holy Spirit at work in their lives.