Vocal prayer, founded on the union of body and soul in human nature, associates the body with the interior prayer of the heart, following Christ's example of praying to his Father and teaching the Our Father to his disciples.
-Catechism of the Catholic Church, 2722
2700 Through his Word, God speaks to man. By words, mental or vocal, our prayer takes flesh. Yet it is most important that the heart should be present to him to whom we are speaking in prayer: "Whether or not our prayer is heard depends not on the number of words, but on the fervor of our souls."2
2701 Vocal prayer is an essential element of the Christian life. To his disciples, drawn by their Master's silent prayer, Jesus teaches a vocal prayer, the Our Father. He not only prayed aloud the liturgical prayers of the synagogue but, as the Gospels show, he raised his voice to express his personal prayer, from exultant blessing of the Father to the agony of Gethsemani.3
2702 The need to involve the senses in interior prayer corresponds to a requirement of our human nature. We are body and spirit, and we experience the need to translate our feelings externally. We must pray with our whole being to give all power possible to our supplication.
2703 This need also corresponds to a divine requirement. God seeks worshippers in Spirit and in Truth, and consequently living prayer that rises from the depths of the soul. He also wants the external expression that associates the body with interior prayer, for it renders him that perfect homage which is his due.
2704 Because it is external and so thoroughly human, vocal prayer is the form of prayer most readily accessible to groups. Even interior prayer, however, cannot neglect vocal prayer. Prayer is internalized to the extent that we become aware of him "to whom we speak."4 Thus vocal prayer becomes an initial form of contemplative prayer.
Examples of vocal prayer include basic prayers such as the Our Father, Hail Mary, Glory Be, etc. and also the words in the silence of our mind that we speak to God. The majority of people know only this (vocal) form of prayer because we do it with our voices. Vocal Prayer is wonderful and we need to practice it. However, it is not enough to nourish our soul. We like to speak to God through our vocal prayers, but we must learn to speak with God, which implies not only speaking, but also listening. Sometimes, if we don't pay attention, we run the risk of saying prayers without actually even praying. To learn to speak with God, we need to learn another form of prayer: Meditation.
Above information taken from the Catechism of the Catholic Church, 2700-2704.
2. St. John Chrysostom, Ecloga de oratione 2: PG 63, 585.
3. Cf. Mt 11:25-26; Mk 14:36.