a) What are the kinds of punishment due to sin, and what are indulgences?
The two kinds of punishment due to sin are: first, eternal punishment of hell due to unforgiven mortal sins; and second, temporal punishment, meaning, it lasts only for a time (either in this life or in purgatory), due to venial sins and also to mortal sins after they have been forgiven.
An indulgence is the taking away of the temporal punishment, either of oneself or of souls in purgatory, through certain prayers or works prescribed by the Church. There are two kinds of indulgences: first, a plenary indulgence is the remission of all the temporal punishment, and can be gained only once a day; second, a partial indulgence is the remission of part of the temporal punishment, and can be gained several times a day. The Church grants indulgences by applying to us from her spiritual treasury the merits of Christ and the saints.
b) How could an Altar Server gain indulgences?
To gain any indulgence we must be free from mortal sin, have at least a general intention of gaining the indulgence, and perform the works required by the Church. To gain a plenary indulgence we must also go to Confession (one Confession within a week before or after allows us to gain several plenary indulgences), receive Holy Communion (once for each plenary indulgence), pray for the Pope’s intentions, and be detached from all sin.
We can gain plenary indulgences when we visit the Blessed Sacrament for at least an hour; read the Bible for at least half an hour; pray the Holy Rosary in a church or with the family; receive or attend another’s First Communion; attend a priest’s first solemn Mass or his 25th, 50th, or 60th anniversary Mass; make the Way of the Cross on Good Friday; renew one’s baptismal promises during the Easter Vigil or on the anniversary of one’s baptism; do spiritual exercises for at least three days; devoutly receiving a Papal blessing including those imparted at Easter and Christmas, and received through live transmission by radio, television, or Internet, etc. Partial indulgences, on the other hand, may be gained by using blessed objects, prayers, sacrifices, acts of service, and other good works.