No. 1422 , 1423, and 1424, page 357 and 358 of the Catechism of the Catholic Church: The Celebration of the Christian Mystery; Chapter Two - The Sacraments of Healing; Libreria Editrice Vaticana: Urbi Et Orbi Communications:
It is called the sacrament of Penance, since it consecrates the Christian sinner's personal and ecclesial steps of conversion, penance, and satisfaction.
It is called the sacrament of confession, since the disclosure or confession of sins to a priest is an essential element of this sacrament. In a profound sense it is also a "confession" - acknowledgment and praise - of the holiness of God and of His Mercy toward sinful man.
It is called the sacrament of forgiveness, since by the priest's sacramental absolution God grants the penitent "pardon and peace."
It is called the sacrament of Reconciliation, because it imparts to the sinner the love of God Who reconciles: "Be reconciled to God." He who lives by God's merciful love is ready to respond to the Lord's call: "Go; first be reconciled with your brother."
From the Baltimore Catechism No. 3; Benziger Brothers, Inc. and Tan Books and Publishers, Inc. Nos. 733 and 735, page 152 and 153.
Q. How do you know that the priest has the power of absolving from the sins committed after Baptism?
A. Because Jesus Christ granted that power to the priests of His Church when He said: "Receive ye the Holy Ghost. Whose sins you shall forgive, they are forgiven them; whose sins you shall retain, they are retained."
Q. Was the power to forgive sins given to the apostles alone?
A. The power to forgive sins was not given to the apostles alone, because it was not given for the benefit merely of those who lived at the time of the apostles, but for all who, having grievously sinned, after Baptism, should need forgiveness. Since, therefore, Baptism will be given till the end of time, and since the danger of sinning after it always remains the power to absolve from such sins must also remain in the Church till the end of time.