To begin the simulation, click on the Erupt button on the left side of the screen. To pause the eruption at any time, click on stop. Once you have stopped, you may continue the simulation by clicking on Continue. Note that if you have made any adjustments to the simulation's parameters they will not take effect until you restart the simulation by clicking Erupt button.
You can zoom in and out of the simulation by dragging the mouse over the main display area.
You can experiment with the parameters by clicking on the Adjustments button.