I’ve heard of how Saint Augustine was sinful , but what was this thing he followed and what did he do?
I would suggest reading his Confessions. It is a great book. Augustine did not become a Christian well into his adulthood. He dabbled in different heretical teachings and he had a mistress and fathered a child out of wedlock. His mother Monica, prayed for him for years and years until he finally was baptized.
I also suggest reading his confessions. He was a very brilliant young man who spent his youth and into his adulthood in dissipations (like having a mistress) and being part of the Manchean sect. It was sermons of the great St Ambrose (and his mother’s constant prayers) that turned his life around. He famously said “Lord give me chastity, but not yet” because it was so hard for him to break off from his mistress. He did ensure that his child was cared for, although I believe that both the mistress and child died young. St Augustine became a priest and the bishop of Hippo (in Algeria).