In the Sacrament of Holy Orders, or Ordination, the priest being ordained vows to lead other Catholics by bringing them the sacraments (especially the Eucharist), by proclaiming the Gospel, and by providing other means to holiness.
Understanding the Sacrament of Holy Orders
USCCB Information of Holy Orders and Vocations
Holy Orders: Ordained to Serve, Gather, Transform, and Send
Diocese of San Diego: Office of Vocations