The Rosary joins repeated prayers with meditation on events in the lives of Jesus and Mary. A decade includes an Our Father, ten Hail Marys and a Glory Be while contemplating a mystery.
A little more context
You may begin by learning one decade and then build toward five. Attention will wander; gently return to the mystery. Beads help keep your place, but being unfamiliar with them does not prevent you from beginning.
A practical beginning
Choose a quiet moment and open the guided Rosary on Life of the Saints. Read the mystery before you start the prayers. If praying with children, allow one person to lead and another to announce the mystery.
Source & further reading
Holy See: Rosary mysteries and the prayer of a decade (opens in a new tab)↗Teaching summaries are introductions. Follow the linked Church source for its fuller context.