Discuss the main stages of Augustine’s intellectual and spiritual development (his student years in Carthage, his Manichean years, his encounter with Ambrose in Milan).
This a great question. Let me give you a brief sketch of the life of Augustine.
First, he was born on November 13, 354 in North Africa (now Algeria). His father was a minor official and a pagan; his mother was a devout Christian, but she was unable to persuade her son to be baptized at an early age. So, we can say that for the most part Augustine grew up as a pagan.
Second, in 370 he went off to Carthage for further studies. While he was there, he confessed to living in sin. He lived with a woman and even had a child with her. His son's name was: Adeodatus.
Third, in 373 he became a confirmed Manichean. Part of the reason for his adherence to Manicheism was due to his intellectual interests. He followed in this religion for nine years, but this did not satisfy him. He not only disagreed with their cosmology, but he also was unimpressed with one of their celebrated bishops, Faustus.
In 383 he made his way to Italy and heard Ambrose, a Christian bishop and this marked the beginning of his Christian walk. in 386 he made a clear confession of his sin and "found" God. In the following year he was baptized by Ambrose and from then on, he grew to be the great bishop of North Africa.