A plenary indulgence (the forgiveness of all temporal punishment from sins that have already been confessed) is granted on the Feast of Divine Mercy to all the faithful who go to Confession, receive Holy Communion, pray for the intentions of the Holy Father, and "in any church or chapel, in a spirit that is completely detached from the affection for a sin, even a venial sin, take part in the prayers and devotions held in honor of Divine Mercy, or who, in the presence of the Blessed Sacrament exposed or reserved in the tabernacle, recite the Our Father and the Creed, adding a devout prayer to the merciful Lord Jesus (e.g. 'Merciful Jesus, I trust in you!').
A partial indulgence (the remission of some temporal punishment from sin) is granted to the faithful "who, at least with a contrite heart, pray to the merciful Lord Jesus a legitimately approved invocation."
For more information on the Feast of Divine Mercy, see the Divine Mercy Sunday page and the Divine Mercy page under Devotions.