Seraphim are angels. As Isaiah explains, they have six wings and their privilege is to attend the throne of God and sing praises to His name. The following quotes help us understand the beings around the throne of God. Elder McConkie explains the term seraphim and Joseph Smith explains the other varied beasts which attend the throne of God.
Bruce R. McConkie
"Seraphs are angels who reside in the presence of God, giving continual glory, honor, and adoration to him. ’Praise ye him, all his angels: praise ye him, all his hosts.’ (Ps. 148:2.) It is clear that seraphs include the unembodied spirits of pre-existence, for our Lord ’looked upon the wide expanse of eternity, and all the seraphic hosts of heaven, before the world was made.’ (D. & C. 38:1.) Whether the name seraphs also applies to perfected and resurrected angels is not clear. While petitioning on behalf of the saints, the Prophet prayed that ’we may mingle our voices with those bright, shining seraphs around thy throne, with acclamations of praise, singing Hosanna to God and the Lamb!’ (D. & C. 109:79.)
“In Hebrew the plural of seraph is seraphim or, as incorrectly recorded in the King James Version of the Bible, seraphims. Isaiah saw seraphim in vision and heard them cry one to another, ’Holy, holy, holy, is the Lord of hosts; the whole earth is full of his glory.’ (Inspired Version, Isa. 6:1-8.) The fact that these holy beings were shown to him as having wings was simply to symbolize their ’power, to move, to act, etc.’ as was the case also in visions others had received. (D. & C. 77:4.)” (Mormon Doctrine, pp. 702-3)
Joseph Smith
"John saw curious looking beasts in heaven; he saw every creature that was in heaven,-all the beasts, fowls and fish in heaven,-actually there, giving glory to God. How do you prove it? (See Rev. 5:13.) ’And every creature which is in heaven, and on the earth, and under the earth, and such as are in the sea, and all that are in them, heard I saying, Blessing, and honor, and glory, and power, be unto Him that sitteth upon the throne, and unto the Lamb for ever and ever.’
“I suppose John saw beings there of a thousand forms, that had been saved from ten thousand times ten thousand earths like this,— strange beasts of which we have no conception: all might be seen in heaven. The grand secret was to show John what there was in heaven. John learned that God glorified Himself by saving all that His hands had made, whether beasts, fowls, fishes or men; and He will glorify Himself with them.” (Teachings of the Prophet Joseph Smith, p. 291)