The application in itself is very minimal, but can be expanded to control parameters in other applications like Ableton Live:
Set the height and width of the rectangle using the sliders
Click record and prepare a distinct facial expression. Once recording, your training examples will contain containing your selected facial features (gestures, orientation and/or raw points) and the current width and height of the rectangle.
Repeat step 1-2 with different width and height values for the rectangle and different expressions
Click train to train the model
Move your face and see the changes in rectangle width and height
The video below takes you through the steps of the training process.