Hands, posture and finger numbers
Nobody wants to spend time on this. It is worth ten minutes anyway, and here is the selfish reason why.
Nobody wants to spend time on posture. It feels like the boring part before the playing starts.
It is worth ten minutes anyway, for one selfish reason: bad hand position does not slow you down at first, it slows you down in about four months, at exactly the point where things were starting to get interesting. Fixing it then means unlearning something. Getting it roughly right now costs almost nothing.
This is step two of the piano path. Step one was finding your way around the keyboard.
Finger numbers
Piano music writes little numbers above or below the notes. They are not note names and they are not fingerings you can ignore — they tell you which finger to use.
Thumb is 1, index 2, middle 3, ring 4, little finger 5. On both hands. The numbering starts at the thumb and counts outward, which means it mirrors: your two number-fives are the two fingers furthest apart.
Almost everyone assumes at least once that the left hand counts the other way. It does not.
Why the numbers are there at all
Because most passages have exactly one fingering that works, and several that get you stuck. Follow the printed fingering and your hand ends up in position for the next few notes. Ignore it and you will find yourself needing a sixth finger.
Editors put real thought into those numbers. Early on, treat them as instructions rather than suggestions.
Sitting
Sit at the middle of the keyboard, far enough back that your elbows are slightly in front of your body rather than pinned at your sides. Elbows roughly level with the keys, or a touch above.
If your bench is too low your wrists drop below the keys, which is the single most common problem and the cause of most beginner hand pain. Too low is far more common than too high. A cushion is a completely legitimate fix.
The shape of the hand
Curve your fingers. The classic instruction is to imagine holding a tennis ball, or to let your arm hang loose at your side and notice the shape your hand naturally falls into — that is very close to correct.
Play with the fingertips, not the flat pads. Keep the wrist level with the forearm, neither dropped nor arched. The knuckles stay up rather than collapsing inward.
What it should feel like
Loose. Almost lazy. If your forearm is tense between notes, something is being held that does not need to be held.
The test: play five notes, then stop and notice your shoulders. If they have crept upward, reset. Tension travels, and it always starts somewhere other than where it hurts.
Pain is information
Fingertips feeling tired after a long session is normal, especially on weighted keys.
Pain in the wrist, forearm or thumb joint is not. That is technique, and it does not improve with practice — it gets worse, because you are repeating the thing causing it. If a position hurts, stop and change it rather than pushing through.
This is the one area where the usual advice about persistence is actively wrong.
Five minutes that will do it
Put your right thumb on middle C and let the next four fingers fall on D, E, F and G. One finger per key, no stretching, no moving the hand.
Play 1-2-3-4-5 up, then 5-4-3-2-1 down, slowly, saying the finger numbers out loud. Then the same with the left hand, thumb on middle C going down: C, B, A, G, F.
Watch your wrist rather than your fingers while you do it. That is the whole exercise, and it is the position almost all beginner music starts from.