Press the green flag. The pencil will then be following your mouse. To draw, press the left mouse button, and hold it down while dragging your mouse over the white space of the canvas. To erase, press the magic wand and do the same as you would to draw. To change the color, press on any of the colors and draw on the canvas. And to chance the size, press the black button and draw. To change it back, press the button next to the black one. You can also change the size of the eraser by clicking that button, and then pressing the magic wand.
I used the same course that I used for my "Flappy Bird" project.
