Christ

And in Jesus Christ, His only son
The Creed has an overall form based on the Trinity. Thus it deals first with the Father, then the Son, and finally the Holy Spirit. I'm not going to deal with the Trinity and Incarnation in detail here because there are separate pages for each. However some minimal explanation is necessary.
While the Gospels show Jesus as having a role beyond a normal teacher, most of Jesus' actions and teachings were appropriate for a First Century Jewish teacher. One of the major developments in scholarship about Jesus during the last few decades has been a reassessment of his relationship to Judaism. It is now clear that Jesus was an observant Jew, as such was defined at the time. His teachings generally fit into First Century Judaism. The main exception is his own personal role. That went beyond anything that Judaism as a whole was willing to accept. Some scholars maintain that this role was not intended by Jesus himself, but developed after his death and was read back into the accounts of his life. I personally believe this is false, as I will indicate below. That is, I believe that Jesus did actually intend something like the role that Christians attribute to him.
Christians see Jesus as in some sense embodying God. This is based on his teachings and actions, as well as on further discussions within the Christian community. Every account we have of Jesus sees him as playing a role beyond that of a normal teacher. Different sources express it differently. In some of the Gospels it is implicit in the way Jesus acts: he forgives people's sins, something that only God can do. In the Gospel According to John, he says "I and the Father are one" and "he who has seen me has seen the Father". However he clearly is a normal human being, who sees God as distinct from himself.
Based on this sort of evidence, Christians developed two separate but related concepts: the Trinity and the Incarnation. The Incarnation looks at Jesus' relationship to God. There is a separate page about the incarnation. At this point, I'm simply going to quote two texts from the New Testament. These represent two ways that Jesus was understood within several decades of his death:
Long ago God spoke to our ancestors in many and various ways by the prophets, but in these last days he has spoken to us by a Son, whom he appointed heir of all things, through whom he also created the worlds. He is the reflection of God's glory and the exact imprint of God's very being, and he sustains all things by his powerful word. (Heb 1:1-3a)
...his beloved Son, in whom we have redemption, the forgiveness of sins. He is the image of the invisible God, the firstborn of all creation; for in him all things in heaven and on earth were created, things visible and invisible, whether thrones or dominions or rulers or powers--all things have been created through him and for him.... For in him all the fullness of God was pleased to dwell, (Col 1:14-16, 19)
There are two things to note in these passages. The first is that Jesus is seen as a human vehicle for God to be present. Note that in these passages there is both a distinction between Jesus and God, and an identification of Jesus with God. Jesus is a human being. But he is God's way of being present as a human being. He embodies God completely.
The other thing to note is that Christ is seen as "pre-existent". That is, creation was done through him. While he was born sometime around 3 BC, there was also a sense in which that human being embodies something that was around before the world was created. The best-known treatment of this is the beginning of John's Gospel:
In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things came into being through him, and without him not one thing came into being. ... And the Word became flesh and lived among us, and we have seen his glory, the glory as of a father's only son, full of grace and truth. (John 1:1-3a, 14)
Thus Christ is seen in two ways. In pre-existent form he is God's creative power, who was always with God and in fact part of him. As such, he is one of the Trinity. However he was born as a human being in history.