“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].

The essential rite of this sacrament for all three degrees consists in the bishop’s imposition of hands on the head of the ordained and his specific consecratory prayer asking God for the outpouring of the Holy Spirit and his gifts proper to the ministry to which the candidate is being ordained.

Common Priesthood of the Faithful
“Though they differ from one another in essence and not only in degree, the common priesthood of the faithful and the ministerial or hierarchical priesthood are nonetheless interrelated: each of them in its own special way is a participation in the one priesthood of Christ. The ministerial priest, by the sacred power he enjoys, teaches and rules the priestly people; acting in the person of Christ, he makes present the Eucharistic sacrifice, and offers it to God in the name of all the people. But the faithful, in virtue of their royal priesthood, join in the offering of the Eucharist. They likewise exercise that priesthood in receiving the sacraments, in prayer and thanksgiving, in the witness of a holy life, and by self-denial and active charity.” [Lumen Gentium, 11]

More information on the Sacrament of Holy Orders (from the Compendium of the Cathechism of the Catholic Church) is available here.