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.If we were to look through scripture for examples of ordination, we would first need to know what we were looking for. This describes the actions called for during ordination:
1544 Everything that the priesthood of the Old Covenant prefigured finds its fulfillment in Christ Jesus, the "one mediator between God and men." The Christian tradition considers Melchizedek, "priest of God Most High," as a prefiguration of the priesthood of Christ, the unique "high priest after the order of Melchizedek"; "holy, blameless, unstained," "by a single offering he has perfected for all time those who are sanctified," that is, by the unique sacrifice of the cross.
1545 The redemptive sacrifice of Christ is unique, accomplished once for all; yet it is made present in the Eucharistic sacrifice of the Church. The same is true of the one priesthood of Christ; it is made present through the ministerial priesthood without diminishing the uniqueness of Christ's priesthood: "Only Christ is the true priest, the others being only his ministers."
1548 Christ is the source of all priesthood: the priest of the old law was a figure of Christ, and the priest of the new law acts in the person of Christ.
1554 "The divinely instituted ecclesiastical ministry is exercised in different degrees by those who even from ancient times have been called bishops, priests, and deacons." Catholic doctrine, expressed in the liturgy, the Magisterium, and the constant practice of the Church, recognizes that there are two degrees of ministerial participation in the priesthood of Christ: the episcopacy and the presbyterate . The diaconate is intended to help and serve them. For this reason the term sacerdos in current usage denotes bishops and priests but not deacons. Yet Catholic doctrine teaches that the degrees of priestly participation (episcopate and presbyterate) and the degree of service (diaconate) are all three conferred by a sacramental act called "ordination," that is, by the sacrament of Holy Orders:
Let everyone revere the deacons as Jesus Christ, the bishop as the image of the Father, and the presbyters as the senate of God and the assembly of the apostles. For without them one cannot speak of the Church.
1581 This sacrament configures the recipient to Christ by a special grace of the Holy Spirit, so that he may serve as Christ's instrument for his Church. By ordination one is enabled to act as a representative of Christ, Head of the Church, in his triple office of priest, prophet, and king.
1582 As in the case of Baptism and Confirmation this share in Christ's office is granted once for all. The sacrament of Holy Orders, like the other two, confers an indelible spiritual character and cannot be repeated or conferred temporarily.
1584 Since it is ultimately Christ who acts and effects salvation through the ordained minister, the unworthiness of the latter does not prevent Christ from acting. St. Augustine states this forcefully:
As for the proud minister, he is to be ranked with the devil. Christ's gift is not thereby profaned: what flows through him keeps its purity, and what passes through him remains dear and reaches the fertile earth.... The spiritual power of the sacrament is indeed comparable to light: those to be enlightened receive it in its purity, and if it should pass through defiled beings, it is not itself defiled.
1573 The essential rite of the sacrament of Holy Orders for all three degrees consists in the bishop's imposition of hands on the head of the ordinand and in the bishop's 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.Our priests and bishops are our shephards on this earth, and without them we would not have the most precious of the sacraments, the Eucharist. We should remember to pray for priestly vocations, and especially to keep our own local bishops, priests and deacons in our prayers.
There's more about the three tiered priesthood in the Old Testament and its fulfillment in the New Testament here.
Brothers, select from among you seven reputable men, filled with the Spirit and wisdom, whom we shall appoint to this task, whereas we shall devote ourselves to prayer and to the ministry of the word." The proposal was acceptable to the whole community, so they chose Stephen, a man filled with faith and the holy Spirit, also Philip, Prochorus, Nicanor, Timon, Parmenas, and Nicholas of Antioch, a convert to Judaism. They presented these men to the apostles who prayed and laid hands on them. (Acts 6:3-6)
While they were worshiping the Lord and fasting, the holy Spirit said, "Set apart for me Barnabas and Saul for the work to which I have called them." Then, completing their fasting and prayer, they laid hands on them and sent them off. (Acts 12:2-3)
Do not neglect the gift you have, which was conferred on you through the prophetic word with the imposition of hands of the presbyterate. (1 Tim 4:14)