Holy Orders is a call from God, not to be confused with a career choice or a right that anyone can invoke. Like Matrimony, it is a Sacrament of Service or Vocation. Unlike the Sacraments of Initiation (Baptism, Confirmation, Eucharist), which are intended for everyone in the Church, Holy Orders is a call given only to some and only to men. It is a gift given as God wills and the Church confirms, not because of what a man can do but because of what he has become through ordination.
There are three degrees of Holy Orders in the Catholic Church: Bishop, Priest, and Deacon.
Jesus calls us as his disciples to a new way of life—the Christian way of life—of which stewardship is a part. But Jesus does not call us as nameless people in a faceless crowd. He calls individually, by name. Each one of us—clergy, religious, layperson, married, single, adult, child—has a personal vocation. God intends each one of us to play a unique role in carrying out the divine plan. The challenge, then, is to understand our role—our vocation—and to respond generously to this call from God. Christian vocation entails the practice of stewardship. In addition, Christ calls each of us to be stewards of our personal vocations, which we receive from God. —from the United States Catholic Catechism for Adults