for better understanding, example if you left handed: whe you wanna catch a glass wich is started falling down from the table (on your left side of course), naturally, you will move to the glass with your LEFT leg first! And then your right leg follow your left leg. But in table tennis, when the glass falling down, you will move to the direction with your RIGHT leg first, and then the LEFT leg follow your right leg.... :) If you speed up this, you get the double step movement footwork technique...sorry for my english