Ordination (or Holy Orders) is the Sacrament for those who have been called to a special ministry of service in the Church.
Holy Orders is the sacrament through which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time: thus it is the sacrament of apostolic ministry. It includes three degrees: episcopate, presbyterate, and diaconate.
Catechism of the Catholic Church, 1536
Three Degrees of Holy Orders
Diaconate
The deacon (Greek: diakonos) is the ordinary minister of Baptism and may lead wedding and funeral services. The deacon also preaches at Mass and attends to the pastoral care of the people.
Presbyterate
In addition to the faculties and duties of the deacon, a priest (Greek: presbuteros) may celebrate the Mass, hear Confession, and anoint the sick. If delegated by his bishop, the priest may also confer Confirmation.
Episcopate
The bishop (Greek: episkopos) is a successor of the apostles and possesses the fullness of the Sacrament of Holy Orders. He therefore has the faculty to celebrate all Seven Sacraments. The duties most unique to him are to ordain priests and deacons, as well as to confer Confirmation as the apostle in the diocese.