The golden ring in The Magician's Nephew is a magical ring, enabling the wearer to disappear into another world. Digory's creepy Uncle Andrew tricks Polly into touching the ring which causes her to vanish. Andrew then explains that Digory may follow her by touching a similar golden ring, and upon arrival, use two green rings to return to their home world. When Digory uses the golden ring, he finds Polly in a shadowy wood, which they dub "the wood between the worlds;" the other-worldly place is full of mysterious pools, each of which leads to another world.
In The Magician's Nephew, the golden ring signifies the transition from the exposition of the story to the rising action; Digory and Polly's use of the ring sets in motion all of the events in the story to come.