The First Council of Nicaea was held in 325 AD. This is probably the most well known of the ecumenical councils and yet there is so much misinformation about it.
The two claims that are often made is that Jesus was made God by a vote and that Emperor Constantine chose the books of the New Testament. Both are false.
The Nicene Creed does clarify the relationship between the Father and the Son and the Council was called in part, because of the rise of Arianism. But even the Arians did not deny the divinity of Jesus. They just believed that the Son had been created by the Father.
And as for Constantine choosing the books of the New Testament, it was not Constantine who was making theological decisions and as far as we know, the canon of the New Testament was not discussed at the Council.
So what exactly was decided at Nicaea? Part of it was what resulted in the Nicene Creed. They also worked through a number of canons on different topics that the Church had been facing.
If you are interested in what happened at Nicaea and what was decided, I recommend looking at this passage from the Church Fathers.
