Right, this clip’s all about painting straight lines and also not pushing down too hard on your bridge. (If the video’s not showing, please check here for common problems.)
You can see for yourself how the hand just glides along the bridge, rather like a piston on an old-fashioned steam engine.
And now for the second clip, which is …
Be aware of how you move your fingers
Completely different scenario here. (Still your bridge though.) This one’s all about the activity which happens on your bridge even when your hand stays in just one place. You’ll see how your fingers are constantly moving up and down, from side to side. All this is crucial to painting the strokes and shapes you want.