Generally, you don't use a strop to sharpen a blade. You use it to remove the wire edge. As you sharpen a blade, the edge gets very thin and will form a thin sliver that sticks out. It will make the blade feel sharp, but it folds or breaks easily and reduces the cutting ability. Sharpen the blade with progressively finer grits until you have the level you want. Then you strop the blade, pulling so that the sharp edge is facing away from the direction of movement. A few passes, alternating sides, will get rid of any wire edge and leave the blade sharp. If you wish, you can use an abrasive compound - they are very, very fine and will polish the edge a bit.