What we hear of St Patrick comes from the Declaration, which was allegedly written by Patrick himself. It is believed that he was born in Roman Britain (the Roman Empire was occupying Britain at the time so he wasn't an Italian from Italy but from the Roman Empire, quite large at the time) in the fourth century, into a wealthy Romano-British family. His father was a deacon and his grandfather was a priest in the Christian church. According to the Declaration, at the age of sixteen, he was kidnapped by Irish raiders and taken as a slave to Gaelic Ireland.
They say that he spent six years there working as a shepherd and that during this time he "found God". The Declaration says that God told Patrick to flee to the coast, where a ship would be waiting to take him home. After making his way home, Patrick went on to become a priest and went back to Ireland with forgiveness in his heart.