There are several creedal statements in the letters of St. Paul, written in the 1st century, which describe the beliefs held by Christians in the first decades after Jesus.
For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve. Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. Then he appeared to James, then to all the apostles.
1 Cor 15:3-7
And you, who once were alienated and hostile in mind, doing evil deeds, he has now reconciled in his body of flesh by his death, in order to present you holy and blameless and above reproach before him, if indeed you continue in the faith, stable and steadfast, not shifting from the hope of the gospel that you heard, which has been proclaimed in all creation under heaven, and of which I, Paul, became a minister.
Col 1:21-23
The Old Roman Creed, written in the 2nd century represents a very brief summary of Christian belief at that time:
I believe in God the Father almighty;
and in Christ Jesus His only Son, our Lord,
Who was born from the Holy Spirit and the Virgin Mary,
Who under Pontius Pilate was crucified and buried,
on the third day rose again from the dead,
ascended into heaven,
sits at the right hand of the Father,
whence he will come to judge the living and the dead;
and in the Holy Spirit,
the holy Church,
the remission of sins,
the resurrection of the flesh,
[life everlasting].
The Nicene Creed, produced by the Council of Nicea in 325, written mainly to clarify the doctrine of the Trinity, sets out the fundamental Christian belief and is used, with minor variations, to this day.
We believe in one God, the Father, the Almighty,
maker of heaven and earth, of all that is, seen and unseen.
We believe in one Lord, Jesus Christ, the only Son of God,
eternally begotten of the Father, God from God, Light from Light,
true God from true God, begotten, not made,
of one Being with the Father; through him all things were made.
For us and for our salvation he came down from heaven,
was incarnate from the Holy Spirit and the Virgin Mary
and was made man.
For our sake he was crucified under Pontius Pilate;
he suffered death and was buried.
On the third day he rose again in accordance with the Scriptures;
he ascended into heaven and is seated at the right hand of the Father.
He will come again in glory to judge the living and the dead, and his kingdom will have no end.
We believe in the Holy Spirit, the Lord, the giver of life,
who proceeds from the Father [and the Son],
who with the Father and the Son is worshipped and glorified,
who has spoken through the prophets.
We believe in one holy catholic and apostolic Church.
We acknowledge one baptism for the forgiveness of sins.
We look for the resurrection of the dead, and the life of the world to come.
Amen.