The Screw is used to tighten and loosen the hair of the bow. When you are not playing you should loosen the hair so that
the shaft does not get distorted.
You usually play using the full length of the bow hair. Sometimes, you may see
references to playing at the tip or the frog - using only the hair at the appropriate end of the bow, to change the quality of the sound.
Hold the bow with a rounded hand shape, as if holding a tennis ball. Keep your hand relaxed - there is no need to group too tightly.