Hi Wilfrid,
There is a button down on the left (a box with an arrow):
-> when you select this box, you switch between scolling mode (the page scrolls according to your gaze) and the click mode (the mouse is moving according to your gaze and a mouse click is performed when your gaze dwells on the same place for some time, i.e. same timings as the cell activation in the grids)
Julien