1807171. What are the degrees that make up the sacrament of Holy Orders?

324. What place does the sacrament of Holy Orders have in the divine plan of salvation?

This sacrament was prefigured in the Old Covenant in the service of the Levites, in the priesthood of Aaron, and in the institution of the seventy "Elders" (Numbers 11:25). These prefigurations find their fulfillment in Christ Jesus who by the sacrifice of the cross is the "one mediator between God and man" (1 Timothy 2:5), the "High Priest according to the order of Melchizedek" (Hebrews 5:10). The one priesthood of Christ is made present in the ministerial priesthood.

"Only Christ is the true priest, the others being only his ministers." 

(Saint Thomas Aquinas)

Further reading: CCC 1539-1546, 1590-1591

325. What are the degrees that make up the sacrament of Holy Orders?

The sacrament of Holy Orders is composed of three degrees which are irreplaceable for the organic structure of the Church: the episcopate, the presbyterate and the diaconate.
      
Further reading: CCC 1554, 1593