Praying for Departed Souls

The importance of praying for departed souls is mentioned in the Bible, in the Second book of Maccabees: "It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins." (2 Macch. 12, 46). It is possible to obtain a plenary (full) indulgence for departed souls, from November 1 to November 8, by doing all the following: going to the sacramental Confession (and have no attachment to sin, even venial), participating in the Holy Mass and receiving the Holy Eucharist each day we wish to gain the indulgence (but we only need to go to Confession once during the period), reciting the Creed to renew our profession of faith, praying according to the intentions of the Holy Father (one Our Father, one Hail Mary and Glory Be to the Father or other prayer) each day we perform the work of the indulgence, and visiting a cemetery at least once from November 1 to November 8 to pray for the deceased, even mentally.

"An indulgence is a remission before God of the temporal punishment due to sins whose guilt has already been forgiven, which the faithful Christian who is duly disposed gains under certain prescribed conditions through the action of the Church which, as the minister of redemption, dispenses and applies with authority the treasury of the satisfactions of Christ and the saints."
"An indulgence is partial or plenary according as it removes either part or all of the temporal punishment due to sin." Indulgences may be applied to the living or the dead.

(Cathechism of the Catholic Church, X, art. 1471).