The sacrament of Holy Orders was instituted by Christ at the Last Supper. Recipients dedicate themselves towards the salvation of others. This sacrament contributes to the salvation of recipients, but only because the recipients work for the salvation of others.
The grace of the sacrament imprints an indelible character on the soul of the
recipient and configures him to Christ. Only baptized men may receive the sacrament of Holy Orders.
The practice of ordaining only baptized men rests on the decision of Christ to call only men to these orders in the Church. Not even Mary, the Immaculate Conception, was called by Christ to be a deacon, priest, or bishop.
The essential rite of Holy Orders in each of its degrees is the consecratory prayer said by the bishop and the laying of hands on the head of the one to be ordained.
Only bishops can confer the sacrament of Holy Orders. Priests are co-workers of the bishops.
[From Outlines of the Catholic Faith: Teachings, Beliefs, Practices, Prayers, The Leaflet Missal Company, St. Paul, MN, 2011.]