As to Orders. The supreme task which Christ had to fulfill was his priestly work of atonement which he completed as mediator between God and man. By the union in himself of humanity and divinity Christ is by nature the mediator. As a man from among men, Christ is our mediator with the Father; yet he is also capable of offering a worthy sacrifice to God because, by virtue of the union of his human nature with the Second Person of the Godhead, his human actions have in infinite value. In this fullest sense, the priesthood belongs to Christ alone.

But if Christ wished to live on and continue his work in the Church, the first thing he had to do was to provide for the continuance of his sacerdotal and mediatory function. Above all, if Christ wished to renew the sacrifice of the Cross throughout the ages and all over the world as the sacrifice of the New Law in the Holy Mass, he had to allow other men to share in his priesthood. For if there is to be a true sacrifice, there must be a priesthood ordained and authorized by God from whose hands God will accept the sacrifice.
 

The Sacrament of Holy Orders in the Catholic Church includes three orders: bishop, priest, and deacon. In the phrase "Holy Orders", the word "holy" simply means "set apart for some purpose." The word "order" designates an established civil body or corporation with a hierarchy, and ordination means legal incorporation into an order. In context, therefore, a group with a hierarchical structure that is set apart for ministry in the Church.

For Catholics, the church views typically that in the last year of seminary training a man will be ordained to the "transitional diaconate." This distinguishes men bound for priesthood from those who have entered the "permanent diaconate" and do not intend to seek ordination as a priest. Deacons, whether transitional or permanent, receive faculties to preach, to perform baptisms, and to witness marriages. They may assist at the Eucharist or the Mass, but are not the ministers of the Eucharist. After six months or more as a transitional deacon, a man will be ordained to the priesthood. Priests are able to preach, perform baptisms, witness marriages, hear confessions and give absolutions, anoint the sick, and celebrate the Eucharist or the Mass. Some priests are later chosen to be bishops; bishops may ordain priests, deacons, and bishops

Bishops

Are chosen from among the priests in the Catholic Church. Among Eastern Catholic Churches, which permit married priests, bishops must be widowers or unmarried, or agree to abstain from sexual contact with their wives. It is a common misconception that all such bishops come from religious orders. While this is generally true, it is not an absolute rule. Catholic bishops are usually leaders of territorial units called dioceses.

Normally, bishops administer the sacrament of Holy Orders. In Latin-rite Catholic churches, only bishops (and priests with authorization by the local bishop) may licitly administer the sacrament of confirmation, but if an ordinary priest administers that sacrament illicitly, it is nonetheless considered valid, so that the person confirmed cannot be actually confirmed again, by a bishop or otherwise. Latin rite priests with special permission of the diocesan bishop or the Holy See can lawfully administer confirmation; every Catholic priest must administer confirmation, even without permission, to children in danger of death. In Eastern Catholic Churches, confirmation is done by parish priests via the rite of chrismation, and is usually administered to both babies and adults immediately after their baptism. 

Priests

The word either derives ultimately from the Greek πρεσβύτερος/presbuteros meaning "elder" or the Latin praepositus meaning "superintendent." The Catholic Church sees the Priesthood as both a reflection of the ancient Jewish priesthood in the Temple, and the work of Jesus as priest. The liturgy of ordination recalls the Old Testament priesthood and the priesthood of Christ. In the words of Thomas Aquinas, "Christ is the source of all priesthood: the priest of the old law was a prefiguration of Christ, and the priest of the new law acts in the person of Christ" Summa Theologiae III, 22, 4c. Priests may celebrate Mass, hear confessions and give absolution, celebrate Baptism, serve as the Church's witness at the sacrament of Holy Matrimony, administer Anointing of the Sick, and administer Confirmation if authorized to do so by the Bishop. See Presbyterorum Ordinis for the Second Vatican Council decree on the nature of the Catholic priesthood.

Deacons

The Diaconate is one of the three Major Orders in the Catholic Church. The first deacons were ordained by the Apostles in Acts of the Apostles chapter 6. The ministry of the deacon in the Roman Catholic Church is described as one of service in three areas: the Word, the Liturgy and Charity. The deacon's ministry of the Word includes proclaiming the Gospel during the Mass, preaching and teaching. The deacon's liturgical ministry includes various parts of the Mass proper to the deacon, including being an ordinary minister of Holy Communion and the proper minister of the chalice when Holy Communion is administered under both kinds. The ministry of charity involves service to the poor and marginalized and working with parishioners to help them become more involved in such ministry. As clerics, deacons are required to say the Liturgy of the Hours daily; Deacons, like bishops and priests, are ordinary ministers of the Sacrament of Baptism and can serve as the church's witness at the sacrament of Holy Matrimony, which the bride and groom administer to each other. Deacons may also preside over funeral rites outside of Mass, They can preside over various services such as Benediction of the Blessed Sacrament, and they may give certain blessings.

Minor Orders

From the 3rd century AD up until seven years after the Second Vatican Council (1962–1965), the Roman Catholic Church had four minor orders up to the order of subdeacon, which were conferred on seminarians pro forma before they became deacons. The minor orders and the subdiaconate were not considered sacraments, and for simplicity were suppressed under Pope Paul VI in 1972. Only those orders (deacon, priest, bishop) previously considered major orders of divine institution were retained in most of the Latin rite. Previously some included the subdiaconate into the major orders, and excluded mentioning the order of bishop, as this order was seen as the fullness of the priestly order already conferred. The total number of minor and major orders in the pre-1966 structure was however always considered to be seven.