Tutorials for crocheting a magic ring are at Planet June, Craftsy and CraftyDeb. The magic ring is an alternative technique for beginning a crochet in the round.
Crochet in the round is the method for creating circular pieces in order to make hats, mittens, stuffed animals and other items with rounded parts. The crafter begins in the center and works outwards in circles, or rounds. Crochet in the round can begin with a chain of stitches linked together, but this leaves a small hole in the center of the circle. The magic ring provides a beginning for crochet in the round that doesn't have a hole in the center.