From the Catechism of the Catholic Church:
Two participations in the one priesthood of Christ
1546 Christ, high priest and unique mediator, has made of the Church "a kingdom, priests for his God and Father."20 The whole community of believers is, as such, priestly. The faithful exercise their baptismal priesthood through their participation, each according to his own vocation, in Christ’s mission as priest, prophet, and king. Through the sacraments of Baptism and Confirmation the faithful are "consecrated to be . . . a holy priesthood."21
1547 The ministerial or hierarchical priesthood of bishops and priests, and the common priesthood of all the faithful participate, “each in its own proper way, in the one priesthood of Christ.” While being “ordered one to another,” they differ essentially.22 In what sense? While the common priesthood of the faithful is exercised by the unfolding of baptismal grace --a life of faith, hope, and charity, a life according to the Spirit–, the ministerial priesthood is at the service of the common priesthood. It is directed at the unfolding of the baptismal grace of all Christians. The ministerial priesthood is a means by which Christ unceasingly builds up and leads his Church. For this reason it is transmitted by its own sacrament, the sacrament of Holy Orders.