The block starts with your arm pointed down about how you’d be posed if you were saying “Hey, look a quarter on the sidewalk”, but point all your fingers instead of just your index finger. Then you do the ‘wax on’ block from The Karate Kid, moving your hand across your body, up, around, and down, finishing with your hand approximately in front of your shoulder.
But you know...The so called "low block" may not be the original intent either. It slips down so nice for an in tight groin grab (hand certainly is at right height )...It gets under an incoming grab for some interesting applications. It helps you move away from a threat. It can be almost anything and it`s only part of a one movement of many.