What is the origin of the idiom "red herring" and when to use it?

The idiom "red herring" originates from a technique used in training hunting dogs. A red herring is a smoked and strongly scented fish, and it was used to distract or divert the hounds from the scent of the actual prey during training. In a figurative sense, this expression is used to refer to something that is misleading or a distraction, diverting attention away from the real issue or problem at hand.