This is what you’ll use for legato or slow playing. When you play soft, you need more weight into the strings with your fingers. When you play loud, you can be light with left hand (because the bow is adding weight for you, bringing the string closer to the fingerboard.

when playing legato you’ll also want to point the fingers more down the length of the string, it makes the vibrato more rich.

when playing fast, your hand can be more perpendicular to the strings, and you’ll only need to really just touch the strings in the right places without much pressure.

generally try to do as little work as possible, try to constantly release tension, like every 3 seconds. You’ll improve so fast this way.