Holy Orders is the sacrament by which a man is made a bishop, a priest, or a deacon, and thus dedicated to be an image of Christ.
A bishop is the minister of this sacrament. Ordination as a bishop confers the fullness of the sacrament, making the bishop a member of the body of successors of the Apostles, and giving him the mission to teach, sanctify, and govern, along with the care of all the Churches.
Ordination as a priest configures the priest to Christ the Head of the Church and the one essential High Priest, and conferring on him the power, as the bishops’ assistant, to celebrate the sacraments and other liturgical acts, especially the Eucharist.
Ordination as a deacon configures the deacon to Christ the Servant of All, placing him at the service of the bishop, especially in the Church’s exercising of Christian charity towards the poor and preaching of the word of God.
Aspirants to the priesthood are required by canon law (canon 1032 of the Code of Canon Law) to go through a seminary program that includes, as well as graduate level philosophical and theological studies, a formation program that includes spiritual direction, retreats, apostolate experience, etc. The course of studies in preparation for ordination as a permanent deacon is decided by the episcopal conference concerned.