Offices of the Latter-day Saint Melchizedek priesthood
If an adult man joins the Church, he may be called and ordained to hold the lesser Aaronic Priesthood (if he is morally worthy) by those in the Church with authority to do so. After a period of time (usually one year) the man may be called and ordained to receive the Melchizedek Priesthood (again based upon moral worthiness) by those in the Church with authority.
Genesis 14: 18-20
And Melchizedek king of Salem brought out bread and wine; for he was priest of God Most High.
The LORD has sworn and will not change his mind: You are a priest forever, in the Order of Melchizedek.”
Hebrews 7: 1-3
For Melchizedek, king of Salem, priest of the Most High God…first being by interpretation King of righteousness, and after that also king of Salem, which is King of peace; without father, without mother, without descent, having neither beginning of days, nor end of life, but made like unto the Son of God, abideth a priest continually.
Hebrews 5: 7-10
So Christ also did not take upon himself the glory of becoming a high priest. But God said to him, You are a priest forever, in the order of Melchizedek.”and (He) was designated by God to be high priest in the order of Melchizedek.
Hebrews 5: 19-20
We have this hope as an anchor for the soul, firm and secure. It enters the inner sanctuary behind the veil, where Jesus, who went before us, has entered on our behalf. He has become a high priest forever, in the Order of Melchizedek.”
Hebrews 7: 1
This Melchizedek was king of Salem (Jerusalem) and priest of God Most High.
Hebrews 7: 22— 25
But this with an oath, by him that said unto him: The Lord hath sworn and he will not repent: Thou art a priest forever (in the Order of Melchizedek). By so much is Jesus made a surety of a better testament