The 3 children were engaged one ordinary day in their regular chore of tending the sheep. They would later say that before Mary visited them, an angel who identified himself as the "Angel of Peace" and the "Guardian Angel of Portugal" appeared to them 3 times to teach them prayers and invite them to offer sacrifices and spend time in adoration of our Lord. He was preparing them to receive an even greater visitor, Mary, the Mother of God.
Over the course of several months, Mary gave the children 3 secrets, all of which were eventually revealed. The first secret was a vision of hell. The second secret revealed a desire by God to establish a devotion to the Immaculate Heart of Mary. Through this devotion, Mary promised to save souls and bring peace to the world, all through her ability to intercede for us before God. The third and final secret had to do with the death of a pope and other religious figures. Most people think that this event was attempted but not completed in the assassination attempt on Pope St. John Paul II. He himself said he believed his life had saved through Mary's intercession.
Many good and worthwhile books and commentaries have been written about Fatima, and it is a subject worth learning about. Rather than try to summarize the Fatima story here, I would like to point you to some reliable sources for reading about it. It takes a while to work through the events of the apparition and to listen to Mary's message at the same time. The small book The True Story of Fatima is a good place to start. Ignatius Press also published a book called Fatima Mysteries: Mary's Message to the Modern Age, and I also recommend William Walsh's book Our Lady of Fatima.
Although the title usually given to Mary for this apparition is Our Lady of Fatima, her official title is Our Lady of the Holy Rosary at Fatima. That name change makes a big difference. Calling Mary Our Lady of Fatima emphasizes the secrets and the supernatural aspect of Fatima. These are indeed notable, to be sure, but they can also become overwhelming. Remembering that Mary is actually named Our Lady of the Holy Rosary at Fatima gets to the heart of the message. It enables us to carry out the message that Mary relayed - Pray, offer sacrifices and repent. In other words, get out your rosary beads. The solution to war, strife and suffering - literally- lies in your own hands. It is not beyond reach, or too high above us. It is in the humble act of daily prayer.
It is helpful to remember the words of Pope Pius XII who said ""The gates of hell will never prevail, where Mary offers her protection. She is the good mother, the mother of all, and it has never been heard, that those who seek her protection, will not receive it. She will help! Error will be overcome with her assistance and divine grace."
Holy Mary, Mother of God, pray for us now and at the hour of our death.