There is a sad note to be made. As part of the general "spiritual gifts are not important" movement in the church there has been a movement to interpret the keys of the ministering of angels in D&C 13 as meaning the right for mortals to serve in the role of an angel, and to say that such is the meaning of the keys of the ministering of angels referred to in D&C 13. And certainly, there are some scriptures that might lead one to believe that at times mortals serve in the capacity of an angel. The three Holy Men that visited Abraham and destroyed Sodom and Gomorrah by the power of the priesthood were also referred to as angels. But those men were operating in that capacity under the Melchizedek preisthood by which they had power to judge and destroy Sodom and Gomorrah. They exercised the power recorded in the JST at end of Gen 14.
Take the Aaronic priesthood power and authority described in D&C 107:20
D&C 107:20 The power and authority of the lesser, or Aaronic Priesthood, is to hold the keys of the ministering of angels, and to administer in outward ordinances, the letter of the gospel, the baptism of repentance for the remission of sins, agreeable to the covenants and commandments.
Now pair that with the preceding two verses.
D&C 107:18 The power and authority of the higher, or Melchizedek Priesthood, is to hold the keys of all the spiritual blessings of the church—
19 To have the privilege of receiving the mysteries of the kingdom of heaven, to have the heavens opened unto them, to commune with the general assembly and church of the Firstborn, and to enjoy the communion and presence of God the Father, and Jesus the mediator of the new covenant.
These two verses about the Melchizedek priesthood mean exactly what they say. They are talking about man being connected with the powers of heaven, even to the point where he enjoys the presence of God the Father and the Son at times. Reading these two verses make it perfectly clear that when we read in the next verse that "the power and authority of the lesser, or Aaronic Priesthood, is to hold the keys of the ministering of angels", the intention is not about mortals acting in the capacity of angels. It is talking about man being connected with the powers of heaven, and angels appearing to man in precisely the sense that Gabriel appeared to Mary, that Moroni appeared to Joseph Smith, that an angel spoke with Elijah, or Zacharias, or Nephi, or any of the other numerous times in the scriptures when an angel appeared to a mortal man.