Complex sentence: He first created a group of angelic beings, called in Elvish the Ainur, and these holy spirits were co-actors in the creation of the universe through a holy music and chanting called the "Music of the Ainur", or Ainulindalë in Elvish.
Split into simpler sentences: He first created a group of angelic beings, called in Elvish the Ainur. These holy spirits were co-actors in the creation of the universe through a holy music and chanting called the "Music of the Ainur", or Ainulindalë in Elvish.