The Divine Mercy Novena was given to St. Faustina and runs from Good Friday to Divine Mercy Sunday (Sunday after Easter). The prayers for the Novena may be found at the Divine Mercy Novena Website.
A special note on Divine Mercy Sunday---on this day the faithful can gain a plenary indulgence by doing the following:
1. go to Confession
2. receive Communion
3. pray for the intentions of the Pope
4. pray the Apostles' Creed and the Our Father
5. recite a devout prayer (e.g. Merciful Jesus, we trust in You)
For those who may be impeded from doing the above (e.g. no access to church), other actions may be performed as described in the Vatican's decree.
For how to do this with closed churches because of the coronavirus pandemic, click here.
A short explanation of the plenary indulgence and its link to Divine Mercy Sunday may be found here.