First, the warning:
CAUTION: Do not use in moving vehicle. Do not throw coils out any window. Keep Slinky away from face and eyes.
Now the instructions, and pay attention because they are complicated:
TO BOUNCE SLINKY UP AND DOWN: Hold a few coils tightly in one hand, allowing rest of Slinky to hang down. Now in a bouncing motion, move hand slowly up and down.
So that’s how you do it. I never could figure that out. I was always holding it up. Duh.