The Church does not limit her prayer to only the official Liturgy (Mass and Divine Office) and the celebration of the other Sacraments. The Christian faithful are encouraged to pray at all times from the heart. It is perfectly appropriate to make use of formalized prayers apart from the Church's Liturgy in order to help us develop both a good habit of prayer and a sense of religion.
This is "private", devotional prayer, even if it be carried out together with other people. It is not thought of as an alternative to the public liturgical prayer, but rather as wonderful aid to it. Good devotional prayer flows out of the liturgical experience and then prepares us for going back into it.
Among the Catholic Church's approved devotional prayers the HOLY ROSARY stands out as a most excellent practice, meditating on the various Mysteries of our Redemption and reciting the prayers of the Our Father-Hail Mary-and-Glory-be Doxology in a set pattern (1 Our Father, 10 Hail Mary's, 1 Glory-be constitute a "decade" of the Rosary.) The Rosary may be prayed either privately or recited in common. The Month of October is especially dedicated to the prayer of the Rosary.
Other examples of devotional prayer: the Chaplet of Divine Mercy, the Recitation of Litanies, the May Procession to Our Lady, Novenas, Devotions to the Sacred Heart of Jesus, Prayers Before and After Mass, etc. So many excerpts from the writings of the Saints have become devotional prayers. Catholics have a vast treasury of devotional prayers from which to draw for their own spiritual life.