Turns out, mirror neurons were among the many things discovered by accident.  Some dude was involved in research on the neural activity of monkeys and, one day, mimicked the movement of a monkey.  When the monkey saw him do so, the neural activity was the same as when the monkey made the movement itself.  They were like “golly jee, wowzorz” and looked into it more.

For “learning”, it would apply to things like watching someone hammer a nail or something and you’d see how they did it and be able to replicate the action.