Slicers and people that pull shots, tend to come over the top on the downswing. The results is that the club swings from the outside to in path. If the clubface is open on this path, the ball will fly left to right. If the clubface is closed on this path, the will ball go straight to the left. You will want to learn how to sequence your swing so that you learn to swing the club on the correct plane, so the path is more inside to out. This drill will help you learn to swing the club on the on the correct path.