After Jesus ascended into heaven, he sent down the Holy Spirit. On that day of Pentecost, we began a new era, the age of the Church, during which Christ communicates his work of salvation through the liturgy of his Church, "Until he comes again." Jesus Christ continues his saving work through sacraments of the Church. This is called the Sacramental economy. The liturgical life of the Church revolves around the Eucharistic sacrifice and the seven sacraments. These sacraments include three sacraments of initiation: Baptism, Confirmation and Eucharist; two sacraments of healing: Penance and Anointing of the Sick; and two sacraments at the service of communion: Holy Orders and Matrimony.
The Catechism of the Catholic Church (CCC) #1111, "Christ's work in the liturgy is sacramental: because His mystery of salvation is made present there by the power of His Holy Spirit; Because His body, which is the Church, is like a sacrament (sign and instrument) in which the Holy Spirit dispenses the mystery of salvation; and because through her liturgical action the pilgrim Church already participates, as by foretaste, in the heavenly liturgy." CCC # 1131 "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 disposition."
For a deeper understanding of sacraments in general, please read the Catechism of the Catholic Church, (CCC #1076-1134)
The Sacraments of Initiation: The Sacraments of Initiation include Baptism, Confirmation, and the Eucharist. These are the foundation of every Christian life. Through the grace of these sacraments, the Christian is conformed to Christ. The Christian is born anew in Baptism, strengthened in Confirmation and receives the food of eternal life in the Eucharist. Through these three sacraments, the Christian shares in the divine life and advances in Christian charity. (See CCC #1212)