O blood and water which poured forth from the Heart of Jesus as a Fountain of Mercy for us, I trust in You!
There is an excellent article on the nature of God's mercy and the Divine Mercy here.
And the Fathers of Mercy, at the Chapel of Divine Mercy in Auburn, KY will be having special devotions for this day at 2:00 p.m. There will be opportunity for confession (we have four confessionals, folks!), a blessing of the Divine Mercy image, and a Chaplet of Divine Mercy. And these being mission priests, I'm sure there will be a great talk on the Divine Mercy.