Confessions is an autobiographical account of Augustine's early life and conversion to Christianity.
One can find online versions but I recommend Penguin Classics R. S. Pine-Coffin's translation.
Born in Algeria, Augustine lived in the Roman Empire, in Carthage, Rome, and later Hippo, and became an influential church leader.
In Confessions, Augustine confesses his sin and Manichaeism and describes his conversion to Christianity.
He experienced the fall of the Roman Empire, writing his most famous work, The City of God, which became one of the most influential books in the Western world.
His Confessions helps one understand who God is, the problem of sin, and the need for conversion.