This is a fun exercise that is handier than it seems at first. You'll set up two targets at a distance, and teach your dog to go to either target—left or right—on cue. Later, you will set up similar exercises to bring more general meaning to the cues "left" or "right."
A dog that understands "left" and "right" has a terrific skill for many competition venues including agility, herding, mushing, water dog, and retrieving. This understanding would also be handy walking on trails—and service dog owners could think of a dozen or more applications for "left" and "right."