This devotion to the Our Sorrowful Mother was originated in the Thirteenth century. It recalls the Sorrows the Virgin Mother of God endured in compassion for the suffering and death of her Divine Son.
HISTORY: The Servite Chaplet of the Seven Sorrows is a devotion that recalls seven sorrowful episodes in the life of the Blessed Virgin Mary. The practice originated with the Servite Order (Servants of Mary), probably soon after the Order was founded in Monte Senario, Italy, in 1233.
The traditional symbol of the Seven Sorrows is the Sorrowful Heart of Mary, that is, a heart pierced with seven swords and topped with a flame representing her love for God and for all humanity. The swords refer to the Prophecy of Simeon (Luke 2: 33-35). See the First Sorrow.
PRAYERS: The worshiper prays one "Our Father" and seven "Hail Marys" for each of the Seven Sorrows. The final prayers are: three more "Hail Marys", to honor the tears of the Sorrowful Virgin; one "Our Father", one "Hail Mary", and one "Glory Be" for the intentions of the Pope; an invocation to the Sorrowful Virgin (optional) and a concluding offertory (optional).
BEADS: Like the Holy Rosary, the Seven Sorrows is a "bead-prayer." Servite beads are designed to keep count of the prayers. They are not required to perform the devotion, however. There are 49 beads in the circlet, organized into seven sets of seven beads. Each set is preceded by a medal depicting one of the Seven Sorrows. The beads in the circlet are used to pray the "Hail Mary." The medals in the circlet are used for the "Our Father." The medal for the First Sorrow (The Prophecy of Simeon) closes the circlet. It connects to a pendant string of four more beads, ending with a larger medal depicting the Virgin of Sorrows. The beads in the pendant string represent the final prayers.
To pray the Seven Sorrows using beads: Start with the medal for the First Sorrow (the one that connects the circlet). Follow the beads and medals until you return to the First Sorrow medal. Then skip to the end of the pendant string. Pray one "Hail Mary" on each of the first three beads in the string. Use the last bead, the one closest to the First Sorrow medal, to pray the rest of the final prayers.
Information from: http://www.ixeh.net/faith/Seven-S/ss-00.html