Book Appearances: The Magician’s Nephew
Overview: The yellow and green magic rings in The Magician’s Nephew allow travel to and from the Wood Between the Worlds.
In the story
The magic rings matter because they are the practical mechanism that opens the whole inter-world structure of the series. Without them, Digory and Polly never reach Charn, and Jadis never enters Narnia’s beginning.
They are also a reminder that curiosity and experiment can open doors a person is not morally ready to walk through.