The Sacrament of Holy Orders marks men to stand in the Person of Christ as Servant, and Head. There are three "degrees" of the sacrament: the diaconate (deacons), presbyterate (priests), and the episcopate (bishops).
Married men may discern and enter formation for the Permanent Diaconate, the call to proclaim the Gospel, serve alongside the priest at the altar, administer Baptism, and preside over weddings and funerals.
Single men enter seminary to discern the priesthood, the call to administer the sacraments, and especially offer the Holy Sacrifice of the Mass, consecrating bread and wine into the Body and Blood of Christ for the faithful. Priests live this out in promised celibacy, to be in total conformity to Christ. Priests serve in their own diocese in parishes, or they belong to religious communities with a particular charism, or ministry focus (Dominicans, Franciscans, etc.). The office of Bishop is bestowed on select priests by the Pope to lead dioceses.
For more information, please see the Archdiocese Vocations website below.