Ordination to the priesthood is always a call and a gift from God. Christ reminded his Apostles that they needed to ask the Lord of the harvest to send laborers into the harvest. Those who seek priesthood respond generously to God’s call using the words of the prophet, “Here I am, send me” (Is 6:8). This call from God can be recognized and understood from the daily signs that disclose his will to those in charge of discerning the vocation of the candidate. (from the United States Catholic Catechism for Adults )
Those who are called to be priests are ordained through the Rite of Ordination. In celebrating this Rite, men receive a permanent spiritual mark, called a character, signifying that they represent Jesus’ presence in the Church.
There are three levels of participation in the Sacrament of Holy Orders: as bishop, as priest (from presbyter, which is Greek for “elder”), and as deacon.
A bishop receives the fullness of the Sacrament of Holy Orders. He is the head or Ordinary of the local church. The local area entrusted to him is called a diocese. A bishop is also a member of the episcopal college: this is all the bishops who, with the pope, guide the Church.
Priests serve the community in various ways. They may be called to serve in their dioceses or as religious order priests, carrying out the mission of a particular religious community. They preside at liturgies, preach, administer the sacraments, counsel people, serve as pastors, and teach.
Deacons help and serve bishops by serving the needs of the Church, proclaiming the gospel, teaching and preaching, baptizing, witnessing marriages, and assisting the priest celebrant at liturgies.
Deacons are ordained for service in the Church. There are deacons who are studying to become priests. There are deacons that include married men who are called to remain deacons for life and to serve the Church in this capacity.
Priests receive the Sacrament of Holy Orders in the Rite of Ordination. The bishop lays his hands on the head of the candidate and says a prayer asking for the outpouring of the Holy Spirit. In one part of the rite, the candidate lies in front of the altar while the Litany of the Saints is sung or recited. In another part of the rite, a priest’s hands are anointed with chrism. In the rite for a bishop, the new bishop’s head is anointed.