We first review the ellipse() function and then animate a circle from the left to the right border of the screen. We use a variable to hold the current position of the circle. For doing random animation we don't need a variable because we don't need to know the last position of the object. But for animating an object moving in one direction, we need to know where we are now to know where we will be next. That's why we store the current position in a variable.
This episode was a bit too long and serious. The next one should be shorter and more fun :)