This is the Nicene Creed as it was produced by the Council of Nicaea (or Nicea or even Nice). There were additions made at later councils, especially to the line about the Holy Spirit.
We believe in one God, the Father Almighty, Maker of all things visible and invisible; and in one Lord Jesus Christ, the Son of God, the only-begotten of the Father, that is, of the substance of the Father; God of God and Light of light; true God of true God; begotten, not made, consubstantial with the Father, by whom all things were made, both which are in heaven and on earth: who for the sake of us men, and on account of our salvation, descended, became incarnate, and was made man; suffered, arose again the third day, and ascended into the heavens, and will come again to judge the living and the dead; also in the Holy Spirit. But the holy, catholic [i.e., "universal," not Roman Catholic], and apostolic church anathematizes those who say, "There was a time when he was not," and "He was not before he was begotten," and "He was made from that which did not exist," and those who assert that he is of other substance or essence than the Father, that he was created, or is susceptible of change.
I will explain and give the history line by line.
We believe in one God, the Father Almighty, Maker of all things visible and invisible.
The Nicene Creed was not invented from nothing in A.D. 325. It was based on the "rule of faith" from the church in Caesarea. Before the Council of Nicaea, every church had a statement of faith, taught at baptism.
At least some churches, if not all, would immerse a person three times, once in the name of the Father, once in the name of the Son, and once in the name of the Holy Spirit. The names were not simply pronounced over the person, but a question was asked. For example, using the Nicene Creed, which was simply a "rule of faith" agreed on by all the churches of the Roman Empire, the person baptizing would ask, "Do you believe in one ...