I just got my Magic Trackpad this weekend and, being the Touch UI geek that I am, I immediately took note of the back of the package. As you can see, Apple’s packaging shows you how to perform gestures on your new trackpad. Their notation is quite simple, efficient and easy to understand. Click for a larger image.
Interested in a more robust gesture notation that you can use in your designs? Luke Wroblewski, Dan Willis and I have authored a pretty comprehensive set under Creative Commons license. You can find it here: Touch Gesture Reference Guide