How to Say the Rosary:

The traditional rosary consists of five sets of ten beads (known as decades), each separated by a larger bead. There is an extension from this main circle of the rosary consisting of a crucifix, a large bead, three small beads, and another large bead.

On the crucifix, say the Apostles' Creed.
On the first large bead, say an Our Father.
On the next three beads, say three Hail Marys.
On the second large bead, say another Our Father.
Now you come to the main part of the rosary. Say an Our Father on each of the large beads, and a Hail Mary on each of the fifty small beads. When you finish, you may enter your petitions and say a Hail, Holy Queen.

The rosary is used for meditation on the 15 mysteries of Christ's life. Each decade of the rosary represents a single mystery. Which mysteries you meditate on depends on the day of the week:

On Mondays, Thursdays, and Sundays in Advent and from Epiphany to Lent: The Five Joyful Mysteries
1. The Annunciation (when the Archangel Gabriel announced to Mary that she was with child.)
2. The Visitation (when Mary visited the pregnant Elizabeth).
3. The Nativity (Christ's birth).
4. The Presentation (when Christ was presented at the Temple in accordance with Jewish tradition).
5. Finding in the Temple (when Joseph and Mary found Christ in the Temple teaching the elders).

On Tuesdays, Fridays, and every day during Lent: The Five Sorrowful Mysteries
1. Agony in the Garden (when Christ prayed in the Garden of Gethsemane).
2. Scourging at the Pillar (when Roman soldiers whipped Christ).
3. Crowning with Thorns
4. Carrying of the Cross
5. The Crucifixion

On Wednesdays, Saturdays, and for Sundays from Easter until Advent: The Five Glorious Mysteries
1. The Resurrection
2. The Ascension
3. Descent of the Holy Spirit (when Christ sent the Holy Spirit on his apostles).
4. Assumption of the Blessed Virgin Mary (when Christ took Mary into heaven).
5. Crowning of the Blessed Virgin Mary (when Christ crowned Mary the Queen of Heaven).

Side note: Protestants may find some of these mysteries disconcerting, since they involve beliefs unique to the Catholic Church.

The rosary can also be used for other prayers, such as the Chaplet of Divine Mercy.