Arianism was named after its preacher Arius, a priest of Alexandria in Egypt. Arius taught that god and Jesus were separate beings, which only God the Father was eternal and too pure and infinite to appear on the earth. Arius held that Jesus the son of God was created by God out of nothing as the first and greatest creation, that Jesus was the crowning glory of all creation. Arianism preached that Jesus was inferior to God the father. In a sense Jesus was a type of demi-god.
Arius and his followers believed in one indivisible god, they argued that Jesus was a created being with divine attributes, but was not divine in and of Himself. This was in conflict with the teaching of Bishop Alexander of Alexandria. He argued that there were three persons in the one god, the father, the son and the Holy Spirit. He brought this argument to the First Council of Nicaea in 325, where the Nicene Creed was also produced. The Creed confessed that the Son of God is "begotten, not made, of the same substance as the Father", and condemned Arius, who had affirmed that the Son of God "came to be from things that were not" and that he was "from another substance" than that of the Father. Arianism was condemned by the council and anathematised Arius and his followers.
Arianism is very different to what we believe of Christ today. The Church believes that Christ is fully human and fully divine rather then Jesus being inferior to that of God. According the catechism of the Catholic Church, The truth of Jesus' divinity is confirmed by his Resurrection.