The Latin word sacramentum means "a sign of the sacred." The seven sacraments are ceremonies that point to what is sacred, significant and important for Christians. They are special occasions for experiencing God's saving presence. That's what theologians mean when they say that sacraments are at the same time signs and instruments of God's grace.

In the Sacrament of Holy Orders, or Ordination, the priest being ordained vows to lead other Catholics by bringing them the sacraments (especially the Eucharist), by proclaiming the Gospel, and by providing other means to holiness. Read more »

http://en.wikipedia.org/wiki/Sacraments_of_the_Catholic_Church#Holy_Orders

"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 guide, 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.

See also Catechism of the Catholic Church, 1536–1600"

Main articles: Bishop (Catholic Church), Priesthood (Catholic Church), and Roman Catholic Deacon