Clergy is the name for people who are leaders in their religious community. Their roles and functions vary, but usually they preside over specific rituals. They are also experts, and help establish the doctrines of their faith. Usually, there are specific rituals that make people become part of the clergy. Sometimes, clergy are elected by a group of people. The ritual that make people part of the clergy in Christianity is called ordination or consecration.
Not everyone can become part of the clergy. Different denominations exclude different groups of people.