A sacrament is an outward sign instituted by Christ to give grace. In the 12th century, the tally of seven sacraments achieved acceptance. Sacraments are a means by which the nature and structure of the church are brought into operation.
According to the United States Conference of Catholic Bishops, we recognize that the sacraments have a visible and invisible reality, a reality open to all the human senses, but grasped in its God-given depths with the eyes of faith.
The visible reality we see in the sacraments is their outward expression, the form they take, and the way in which they are administered and received. The invisible reality we cannot "see" is God's grace, his gracious initiative in redeeming us through the death and Resurrection of his Son.
His initiative is called grace because it is the free and loving gift by which he offers people a share in his life, and shows us his favor and will for our salvation. Our response to the grace of God's initiative is itself a grace or gift from God by which we can imitate Christ in our daily lives.
The Sacraments of Initiation
The Sacraments of Healing
The Sacraments at the Service of Communion