The Christian begins his day, his prayers, and his activities with the Sign of the Cross: "in the name of the Father and of the Son and of the Holy Spirit. Amen." the baptized person dedicates the day to the glory of God and calls on the Savior's grace which lets him act in the Spirit as a child of the Father. The sign of the cross strengthens us in temptations and difficulties.
Source: Catechism of the Catholic Church (Vatican.va)