Of course I forgot about alt+mouse over

The first 4 pins are the X coordinate of the pixel (LSD to MSD) and the next 3 are the Y coordinate. (also LSD to MSD).
X goes from left to right, and Y goes from bottom to top.
Then, the next three pins are for the color, in the order red, green, then blue. The next pin writes that pixel to the screen, and the last pin clears it to all white.

How does the screen chip work?

It outputs the key that you're pressing in ASCII.

I downloaded it, and I can't draw

If you decide to delete the game, it's still in AppData. Press Win + R, run "%APPDATA%", then look for a folder called "howtobeatree".

?

huh?