Sacraments are outward signs instituted by Christ, and entrusted to the Church, to give grace.
The Catechism of the Catholic Church gives a basic definition of a sacrament.
The sacraments are efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us. The visible rites by which the sacraments are celebrated signify and make present the graces proper to each sacrament. They bear fruit in those who receive them with the required dispositions. (CCC 1131) Sacraments are “powers that comes forth” from the Body of Christ, which is ever-living and life-giving. They are actions of the Holy Spirit at work in his Body, the Church. They are “the masterworks of God” in the new and everlasting covenant. (CCC 1116)
The Compendium of the Catechism, explains this aspect of sacraments as well.
Sacramental grace is the grace of the Holy Spirit which is given by Christ and is proper to each sacrament. This grace helps the faithful in their journey toward holiness and so assists the Church as well to grow in charity and in her witness to the world. “(231)
The seven sacraments of the Catholic Church all find their origin in the life and ministry of Jesus Christ and in the Church he founded. The sacraments are not something the Church can change, as they come from Jesus himself.”
The seven sacraments instituted by Christ are as follows:
Baptism, Confirmation, Holy Eucharist, Penance, Anointing of the Sick, Holy Orders and Matrimony.