“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.”
Catechism of the Catholic Church 1131
There are seven sacraments; Baptism, Confirmation, Holy Eucharist (Holy Communion), Penance (Confession), Anointing the Sick, Holy Orders and Matrimony.
Within these seven sacraments there are three of initiation (Baptism, Confirmation, and Holy Communion) because the rest of our life as a Christian depends on them.These three are important for the completion of baptismal grace.
There are two for healing (Confession and the Anointing of the Sick).
The remaining two (Marriage and Holy Orders) are for the mission in building up the church.