Imagine the cutter is the wheel off a toy car with a rubber tyre on it on it's spindle, and you are rolling it down the edge of the board whilst holding the other end of the spindle between finger and thumb. Now, whilst still travelling down the edge, turn the spindle between your finger and thumb so that the wheel is going in the opposite direction to the one it will follow if you just roll it along the edge, the tyre is now spinning against the natural direction of rotation and dragging against the wood. This is the direction the cutter must turn, so that the cut pulls the cutter into the wood rather than racing it away down the edge as if it were that little wheel with a motor attached..
The direction you move the router must always be so that the little wheel is spinning in the wrong direction. Hope that helps.