a) What is the second precept of the Church?
The second precept of the Church is: to confess one’s sins, receiving the sacrament of Reconciliation at least once each year.
We should also try to confess whenever we realize that we are still in a state of mortal sin (and not receive Holy Communion meanwhile), or find ourselves in danger of death.
b) Why should an Altar Server know and live the second precept of the Church?
Frequent Confession intensifies our love for God, helps us to overcome temptation, and helps us to remain in the state of grace (that is, free from mortal sin).
The Altar Server should help others through the apostolate of Confession, that is, by explaining this sacrament to them and encouraging them to approach it regularly and frequently.