The set_at () method will plot a single pixel point in the color of your choosing; in this case, the pixel will be white at the coordinates $\mathrm{x}=100$, and $\mathrm{y}=100$. To see this in action, run the script. Remember that you will need to right-click on the filename in the Project window and select Run before you'll be able to run it from the little green icon at the top-right of the window. Now, try plotting another point at $(200,200)$. You can do this with a second set_at () call, for example, as follows:
screen.set_at $((200,200)$, white $)$