Complex sentence: Simulation can be used to model and test a system's behavior, as well providing engineers with a tool for inexpensive, fast, and secure analysis to test how changes in a system can affect the performance of that system.
Split into simpler sentences: Simulation can be used to model and test a system's behavior. Simulation also provides engineers with a tool for inexpensive, fast, and secure analysis to test how changes in a system can affect the performance of that system.