Social interactions are rich, complex, and dynamic. One way to understand these is to model interactions that fascinate us. Some of the more realistic and powerful models are computer simulations. Simple, elegant and powerful, tools are available in user-friendly free software to help you design, build and run your own models of social interactions that intrigue you, and do this on the most basic laptop computer. Focusing on a well-known model of housing segregation, this Element is about how to unleash that power, setting out the fundamentals of what is now known as 'agent based modeling'.