First Book of Enoch: Angels, Watchers and Nephilim
The Book of Enoch tells of the Watchers, a class of angel, who came to earth, taught humans weapons, alchemy, spell potions, sorcery, astrology, and astronomy. The Watchers married humans and produced the Nephilim. For this, they were cast into Tartarus. This is also mentioned in the New Testament. This is an easy to read translation with additional information on angels, Watchers, and Nephilim.