The Sacraments are outward signs instituted by Christ that impart divine grace to those disposed to receive them. The seven Sacraments were instituted by Jesus and His Apostles and form an integral part of what it means to be a Christian. All celebrations of the Sacraments are done through the liturgical life of the Church. (Theologiea III, 65, 3]..
The seven sacraments are grouped into three types:
This grouping, while not the only one possible, does allow us to see that the sacraments form an organic whole in which each particular sacrament has its own vital place. In this organic whole, the Eucharist occupies a unique place as the "Sacrament of sacraments": "all the other sacraments are ordered to it as to their end."
(Catechism of the Catholic Church, para 1210-11; quote is St. Thomas Aquinas, Summa).