Nine days of prayer for one intention.
Choose one intention and one prayer, and keep it for nine consecutive days.
Many novenas precede a feast, ending on its eve. Others are prayed at any time of need.
If you miss a day, pick it back up. Nothing is voided.
Persistence in prayer is commanded, not tolerated. Christ tells the parable of the widow who will not stop knocking. A novena is a structure for not giving up on the third day.
The number comes from the nine days between the Ascension and Pentecost, when the Apostles and Mary remained in the upper room in prayer. That is the first novena and every other one imitates it.
Novenas multiplied in the medieval and modern West, attached to feasts, saints, and needs, and they remain one of the most common forms of Catholic prayer.
Free. There is no mechanism in a novena. God is not moved by the count but by the trust that keeps it.