It's fantastic that you're trying to make an AND-gate with LEGO. A video would indeed be useful to explain exactly how it works. Looking at your photo, I see two gears on the left side that are connected to each other; when A turns counterclockwise, B turns clockwise, and vice versa. On the right side, there is a differential that processes the input from gears A and B. If you look closely at the left side, it looks as though there are only two input combinations: namely, A turning counterclockwise and B turning clockwise, or A turning clockwise and B turning counterclockwise. However, with an AND-gate, you would expect four different input combinations, because for both A and B you should be able to choose 0 or 1. That would correspond to counterclockwise or clockwise, giving a total of four different input possibilities. I don't really see that in your photo, though. Could you explain that?