Hand shape for classical guitar?

It has to be arched. Here's an exercise for you. Start on the treble E string. Index finger presses the first fretboard, middle finger second, ring finger third, pinky fourth, press it and play it, and when you have all your fingers on it, don't move them except for the index finger, which moves up to the B string and presses the first fretboard on that string. Then the middle finger moves up, then the ring finger, the little finger 。。。。 But only move one finger at a time. When all the fingers have moved to the B string, move the index finger down, this time to the second fretboard of the E string, then the middle finger to the third fretboard, and the ring finger fourth 。。。。 Basically, you play the E string to the B string, then move a little to the right when you return to the E string to get to the next fretboard, but the most important thing is to move one finger at a time, and it's best to leave the other fingers alone. This works on your hand shape and finger control.

This graphic is a standard hand gesture.