This document discusses the nature and types of sin, including actual and original sin. It defines actual sin as any willful thought, desire, word, action or omission forbidden by God's law. Actual sins are further divided into mortal and venial sins. Mortal sin is a serious violation of God's law that deprives the soul of sanctifying grace, while venial sin is a less serious offense. The document outlines what makes a sin mortal or venial and how each type of sin harms us. It also discusses occasions of sin and how to avoid sinning through prayer, sacraments and resisting temptation.