display.fillCircle(display.width()/2, display.height()/2, 6, BLACK);
The circle functions take four parameters. The first two parameters are the X/Y coordinates for the center of the circle. In these two examples, the center of the circle is the center of the screen. The third parameter is the radius of the circle, and the last parameter is the color for the circle and also the color to fill the circle in the case of the fillCircle() function.