"Holy Orders is the sacrament through which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time: thus it is the sacrament of apostolic ministry. It includes three degrees: episcopate, presbyterate, and diaconate." - Catechism of the Catholic Church
While all the baptized go through a discernment of vocation, sometimes that discernment leads towards the priesthood and religious life. For more information on vocations, please see the Dallas Diocese website on vocations.