Essentially, they provide a link between the know and the unknown. To illustrate, training for a multi-tasking job might benefit from an orchestra metaphor. A baton could be the prop. In training, there is both factual and conceptual information to impart to the trainees. Metaphors illuminate both types of information.
Props are a way of thinking metaphorically.
They can be toys, gizmos, costumes or tools that are generally recognized. Children's toys, such as Tinker Toys, are great because they suggest construction, show how parts relate to the whole, and indicate shape. They are light, portable, and familiar. People remember stories and anecdotes. Stories express cultural values.