Change the factors with the sliders:
H, T, and O are the hundreds, tens, and ones digits for the first (horizontal) factor; h, t, and o are for the second (vertical) factor.
You will need to zoom out to see products larger than 100 x 40. (Last button on right, thrid button down.) Click at (0,0), where the x and y axes meet, for best results. See NavigatingGeogebra.pdf for a quick guide, or the GeoGebra website for more detailed instructions.
In the U.S., paper-and-pencil multiplication is taught with a method that starts with ones x ones. This diagram shows that ones x ones is a tiny part of the product. Could you invent a multiplication method that starts with the highest place values?
Can you adapt this diagrem/method to multiply decimals? Maybe think of the numbers on the axes as counting hundredths instead of ones (for example, 37 might mean 37 hundredths, or 0.37.)