The Book of Psalms is the prayer book the Church received from Israel and never set down. The hundred and fifty Psalms, and the hundred-and-fifty-first, carry the whole range of the human heart before God: praise and lament, repentance and thanksgiving, the cry of the abandoned and the song of the delivered. Christ Himself prayed them, and from the Cross He prayed them still.
In Orthodox use the Psalter is divided into twenty sections called kathismata, so that in the services the whole book is prayed through in the course of a week, and twice over in Great Lent. The Psalms are not studied first and prayed second; they are prayed, taken onto the lips until they become the voice of one's own heart.
To pray the Psalter is to be given words when one has none, and to have one's own words widened. The Fathers counsel the beginner to take even a few Psalms slowly, daily, until they are known by heart, for a Psalm carried in the memory is a prayer always to hand.