Simulations can play a significant role in helping learners understand complicated concepts. Learning by doing and giving the learner a chance to affect the outcome based on their input is a powerful learning tool. The idea here is to maximize comprehension while making learning fun and ultimately transparent.
Simulations can come in the form of software simulations, engineering simulations, process simulations, learning games, etc. If you are trying to show how something works, a simulation of can be made so the learner clearly sees the inter-workings of the concept.
Simulations can be dropped in to regular web based training courses to help learners understand the concept being presented. They can also be presented as stand-alone learning modules that aim to make learning more experiential and fun.