Which Narnia book by C.S. Lewis describes the creation of Narnia?

The Narnia book by C.S. Lewis that describes the creation of Narnia is The Magician’s Nephew.

Published in 1955, The Magician’s Nephew is the sixth Narnia book by publication order but is commonly placed first in the series’ internal chronology. It follows Digory Kirke and Polly Plummer as they travel between worlds using magical rings made by Digory’s uncle, Andrew Ketterley.

The children witness the birth of Narnia through Aslan’s song. They also encounter Jadis, who later becomes the White Witch, and learn the story behind the lamppost that appears in The Lion, the Witch and the Wardrobe.

The book’s publication order can cause confusion. Lewis’s original sequence began with The Lion, the Witch and the Wardrobe in 1950. Later editions often number The Magician’s Nephew as the first volume because its events occur earliest in Narnian history.