The Catechism of the Catholic Church defines Holy Orders as follows.
(1536) 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.
The Episcopate refers to the Bishops of the Diocese. It is the Catholic teaching that the bishops are successors of the Apostles and as such have a universal mission to teach. It is their particular duty to see that the Gospel is proclaimed everywhere. They possess a three-fold ministry: Priest, Prophet and King.
The Presbyterate refers to Priests who are co-workers with the bishops. Through the sacrament of ordination to the priesthood, priests by the anointing of the Holy
Spirit are signed with a special character and so are configured to Christ the priest in such a way that they are able to act in the person of Christ the head.
The Diaconate refers to Deacons who share in Christ’s mission and grace in a special way. The sacrament of Holy Orders marks them with an imprint (“character”) which cannot be removed and which configures them to Christ, who made himself the “deacon” or servant of all. Among other tasks, it is the task of deacons to assist the bishop and priests in the celebration of the divine mysteries, above all the Eucharist, in the distribution of Holy Communion, in assisting at and blessing marriages, in the proclamation of the Gospel and preaching, in presiding over funerals, and in dedicating themselves to the various ministries of charity.