Press the green flag to start. To erase press the green flag, or shake your device.
If you see this project and don’t know what an etch a sketch is you may be confused. If you don’t here is a brief description: An etch a sketch is usually red with gold letters saying etch a sketch with two white or light gray knobs to drag a spike along the back of the screen which is covered with iron dust resulting in a line being formed where the spike passes over the dust.