Catholics pray the rosary because it's a powerful prayer to God, through His mother, Mary.
Praying the rosary has been a tradition in the Church for a long time. It's a bit fuzzy who made it more formal; some say it was St. Dominic and others say it wasn't. What really matters is that this prayer is super powerful.
Throughout Church history, many popes and saints have highly recommended that we pray the rosary. St. Louis de Montfort said, 'When the Holy Rosary is said well, it gives Jesus and Mary more glory and is more meritorious than any other prayer.'
The rosary begins with the recitation of the Apostle's Creed, an Our Father, three Hail Mary's and a Glory Be. Then there are five decades which each begin and end with an Our Father and Glory Be, and have ten Hail Mary's in between. When you pray the rosary, you meditate on the events in Jesus' life. There are the joyful, luminous, sorrowful, and glorious mysteries.
In various apparitions, Mary has appeared holding a rosary and has asked that we continue to pray this prayer. She always leads us to her Son, and presents our needs before Him. Prayer is about developing our relationship with God, and loving Him more, so it makes sense to get to know Him through the events of the life of Christ that we meditate on during the rosary.
The Catechism of the Catholic Church says:
'Meditation engages thought, imagination, emotion, and desire. This mobilization of faculties is necessary in order to deepen our convictions of faith, prompt the conversion of our heart, and strengthen our will to follow Christ. Christian prayer tries above all to meditate on the mysteries of Christ, as in lectio divina or the rosary. This form of prayerful reflection is of great value, but Christian prayer should go further to the knowledge of the love of the Lord Jesus, to union with him' (CCC 2708).
Rosaries are not just decorations. Battles have been won because people prayed the rosary! There have been hearts converted, and impossible intentions answered too. Your life can only be blessed if you start praying the rosary.
For a wonderful description on how to pray the Rosary - CLICK HERE (EWTN)