The Nicene Creed, while not the only profession of Faith, is the beginning. You can read about its roots at Orthodox Wiki, but we chant this at every Divine Liturgy and it is part of the Church’s Holy Tradition. This is what we profess:
And in one Lord Jesus Christ, the Son of God, the Only-begotten, Begotten of the Father before all ages, Light of Light, Very God of Very God, Begotten, not made; of one essence with the Father, by whom all things were made:
And was crucified also for us under Pontius Pilate, and suffered and was buried;
And ascended into heaven, and sits at the right hand of the Father;
And we believe in one, holy, catholic, and apostolic Church.
We look for the Resurrection of the dead,
And the Life of the age to come. Amen.”