Our Lady asked us to take specific actions on the first Saturday of each month, for five consecutive months in reparation to the Immaculate Heart of Mary.
These actions include the following elements, performed with the intention of reparation for blasphemies against the Immaculate Heart, for at least five consecutive months:
Confession (shortly before or after the First Saturday — so long as the person receives Holy Communion in a state of grace);
Holy Communion received on the First Saturday of each month;
The Holy Rosary, five decades recited sometime during the day; and
Meditating for 15 minutes on the Mysteries of the Rosary (one or more).
Here are several articles which further explain this important devotion:
"... a lot of people have forgotten about the Five First Saturdays devotion, but it’s still relevant today - wars are still going on!" - marian.org
"So I call on everyone who loves Mary to start making the Five First Saturdays a regular part of their prayer life. For anyone who visits the National Shrine of The Divine Mercy in Stockbridge, Massachusetts, on the First Saturday of each month, it’s easy! Pilgrims can go to Confession, pray the Rosary for Life, and attend Mass with the intention of making reparation to Our Lady - as she requested. To fulfill the requirement to meditate for 15 minutes on the Mysteries of the Rosary, you can prayerfully walk the Stations of the Cross on Eden Hill for at least 15 minutes, remaining aware of keeping Our Lady company in spirit throughout her Son’s Passion and Death." - The Divine Mercy