Does forgiving the oppressor absolve him from God's punishment? And does praying against him mitigate his punishment? And what are the recommended religious books for a beginner student of Islamic knowledge?

We advise you to be dutiful and good to your father, to maintain ties with your brothers, and to forgive them. Forgiveness is a quality of the righteous and leads to Allah's forgiveness. The forgiveness of the wronged by their oppressor nullifies their right [to retribution], but it does not nullify Allah's right against the oppressor except through repentance. Supplicating against the oppressor may lessen their sin and punishment, and "whoever supplicates against the one who wronged him has indeed gained victory."