The hips and shoulders rotate around and perpendicular to the spine.
Lay an alignment stick on the ground pointing at your target (target line). Place your ball centered, against the address side of the stick.
Grip your club. Aligning yourself to the target with heels 12” apart. Get into your address position. Place the club face behind the ball. Turn hips and shoulders together along the target line, rotating around and perpendicular to the spine. It will feel like your lead shoulder is moving underneath as the hips and shoulders rotate perpendicular around the spine.