Angels are divided into Spheres, also called Choirs.
>The First Sphere
The first sphere angels serve as the heavenly servants of God the Son incarnated (if you're Christian. Angels appear in other mythologies too).
Seraphim are the highest angelic class and they serve as the caretakers of God's throne and continuously shout praises: "Holy, holy, holy is the Lord of hosts; the whole earth is full of his glory!" According to Isaiah 6:1-8, the Seraphim are described as fiery six-winged beings; with two wings they cover their faces, with another two they cover their feet, and the last two they use to fly.
Cherubim have four faces: one of a man, an ox, a lion, and an eagle. They have four conjoined wings covered with eyes, a lion's body, and the feet of oxen. Cherubim guard the way to the tree of life in the Garden of Eden and the throne of God.
The Ophanim are unusual looking even compared to the other celestial beings plus they are said to be moved by the spirit of other beings, which raises the question if the Ophanim are spiritual beings at all or if they are purely material beings. They appear as a beryl-coloured wheel-within-a-wheel, their rims covered with hundreds of eyes. They are closely connected with the Cherubim instead: "When they moved, the others moved; when they stopped, the others stopped; and when they rose from the earth, the wheels rose along with them; for the spirit of the living creatures was in the wheels."
>The Second Sphere
Angels of the Second Sphere work as heavenly governors of the Ceation by subjecting matter and guiding and ruling the spirits.
>Dominions aka Lordships, Dominations
The Dominions are believed to look like divinely beautiful humans with a pair of feathered wings, much like the common representation of angels, but they may be distinguished from other groups by wielding orbs of light fastened to the heads of their scepters or on the pommel of their swords. The Dominions regulate the duties of lower angels.
>Virtues aka Strongholds
These angels are those through which signs and miracles are made in the world. They appear as Dominions do.
>Powers aka Authorities
The primary duty of the "Powers" is to supervise the movements of the heavenly bodies in order to ensure that the cosmos remains in order. Being warrior angels, they also oppose evil spirits, especially those that make use of the matter in the universe, and often cast evil spirits to detention places. These angels are usually represented as soldiers wearing full armor and helmet, and also having defensive and offensive weapons such as shields and spears or chains respectively. Lucifer was the leader of the Powers.
>The Third Sphere
Angels who function as heavenly guides, protectors, and messengers to human beings. This is where we get to the stereotypical "Angel". God made these more human because these guys interact with us.
>Principalities aka Rulers
The Principalities are the angels that guide and protect nations, or groups of peoples, and institutions such as the Church. The Principalities preside over the bands of angels and charge them with fulfilling the divine ministry. There are some who administer and some who assist. The Principalities are shown wearing a crown and carrying a sceptre.
Not to be confused with Arch Angels (aka Arch-Angels), which are Seraphim, Archangels preside over Angels. These are the big guns when God/YHWH needs some muscle. The ones you're familiar with; Michael, Uriel, Gabriel, etc are Archangels.
The lowest order of the angels, and the most recognized. They are the ones most concerned with the affairs of living things. Within the category of the angels, there are many different kinds, with different functions. The angels are sent as messengers to humanity. Personal guardian angels come from this class.