This info comes from Fallen Angels.....and spirits of the Dark by Robert Masello (part of my private occult collection)
Some of this will seem like Sunday School but I think its important to start from the beginning.
Bright Angel-Lucifer. His name means "light bearer" and he was God's most beautiful angel. He took inordinate pride in his own angelic nature. Eventually his pride became so great he did not want a god and wanted to control his own destiny. He rebelled, recruited and army of equally disenchanted angels and waged war for supremacy. God appointed the archangel Michael as his field commander. Revelation 12:7-9, 12 states what happened. Having been thrown out of heaven he would now bear a new name, Satan (the Hebrew word for "advisary") His new dominion was hell. The angels who had fallen with him (as determined by the 4th Lateran Council in 1215 ad) were now transformed into demons as they fell to earth. With nothing better to occupy their time, they resolved to take out their "great wrath" on mortals too foolish or sinful to resist their temptations.
The Watchers- According to this story, which is more fully recounted in 1 Enoch ( a Hebrew book that did not get included into the Old Testament) there was once an order of angels known as the Watchers. They kept a close eye on the affairs of men. They stayed up all night and studyed the new daughters of the early human race. The sons of God (angels) saw the daughters of men and took them for wives. The Watchers came down to earth and mated and instructed their wives in all sorts of "forbidden" archane arts. Such as Botany, astrology, and astronomy. They showed them how to make magic and weapons, and how to use cosmetics. It says that God was displeased. When the offspring of these angels were born they turned out to be great giants who killed and ate any unlucky humans they caught. Even resorted to killing each other. God enlisted Michael to help wipe out the giants then Michael rounded up the fallen Watcher angels and imprisoned them in the valleys of the Earth where they would stay til they were to be cased into everlasting fire.
In Mark 5:2 through 5-9 we are told that Jesus encountered a man posessed by demons. The man had his dwelling among the tombs...and always, night & day he was in the mountains, and in the tombs crying, and cutting himself with stones. When the man accosted Jesus, Jesus spoke to the demon who posessed him and said, "Come out of the man, thou unclean spirit. And he asked him, What is thy name? And he answered, saying, My name is Legion: for we are many." So how many demons are there? What are their proper names? And what specific powers do they posess? Even Jesus couldn't get a clear answer- and priests, theologians, and demonologists have been debating ever since. When St. Marcarius of Alexandria begged the Lord to let him see the hosts of evil, the Lord obliged- and Marcarius claims that they were as "numerous as bees."
How old are demons? Hesiod, the ancient Greek poet, based his own calculation on the average life span of the phoenix, a mythical bird of great beauty reputed to build its own funeral pyre and then rise from the ashes reborn. The phoenix, Hesiod asserted lived 10X long as a man, and demons lived 10X as long as the phoenix. Thus, he arrived at 6,800 years for the average demonic life. Just a theory.
How were all these demons organized? Who lorded it over whom? Who gave the orders, and who obeyed whom? Just as God has his seraphim, cheribum, and archangels, Satan, too appointed his own unholy aristocracy to help him rule over his kingdom. Beelzebub, Leviathan,Asmodeus, Astaroth (encouraged men to sloth and idleness and was a guidance counselor for other fallen angels ), Behemoth, Belial, were main lords of hell.
6 Kinds of Demons: 1.)Firey- dwell in the upper air and will never descend to the lower regions until the day of Judgement and have no dealings on earth with men. 2.) Aerial- these dwell in the air around us. They can descend to hell and by forming bodies out of the air, can at times be visible to men. They cospire to do for the detstruction of mankind. 3.) Terrestrial- Cast from Heaven to earth for their sins. Some of them live in woods and forests, and lay snares for hunters; some dwell in the fields and lead night travelers astray; some dwell in hidden places and caverns; while others delight to live in secret among men.
4.) Aqueous, dwell under water in rivers and lakes, and are full of anger, turbulent, unquiet and deceitful. They raise storms at sea, sink ships, and destroy life in the water. More often women than men are seen. 5.) Subterranean, live in caves and caverns and in the mountains. They are of a very mean disposition, and chiefly molest miners at work. They cause earthquakes and winds and fires, and shake the foundations of houses. 6.) Heliophobic, hate and detest light. Never appear during daytime nor assume bodily form until night. Are all dark within and shaken with icy passions, malicious, restless, and perturbed. Shun people mostly.
Class will tell duties: Lower demons can be classified into groups of where ley live and what kind of mayhem they like to stir up. 10 main categories devised by the demonologist Alphonsus de Spina: 1. Fates 2. Poltergeists 3. Incubi/ Succubi 4. Marching hosts
5. Familiar demons (eat & drink w/men) 6. Nightmare demons 7. Demons formed during rough sex 8. Deceptive demons (appear as a familiar person) 9. Clean demons (assail only holy men/ women) 10. Demons given to witches.
Thought this info was interesting and might shed more light on the subject.