You will learn more about controllers and graphs in this tutorial.
A controller is a device which allows you to graphically modify a property of a body or a spring. In the tutorial, the controller allows you to change the stiffness of the spring "spring1". By moving the slider to the right or using the W key you can increase spring1 stiffness value and by moving the slider to the left or using the Q key you can decrease it. Right-clicking on the controller brings you several context actions and the Configure Controller... dialog allows you to change each property of the controller.
Graphs allow you to graphically visualize the relationship between two variables. The example in the tutorial prints the evolution of the position of particle1 while time advances in world1. With a right click on a graph you can clear or delete the graph as well as edit the configuration dialog and change here all the properties for this graph.
At the end of this tutorial you are able to use controllers to act on your bodies properties and graphs to monitor specific properties in your experiment.