The hip adductors and abductors are working together to keep the knees over the line of the feet. The lower back and abdominal muscles are contracting to keep the upper body strong and straight. Good posture requires the entire body to work together. And while all this is going on, coordination and balance is developing as the body tells the brain via the nervous system where it is in space. To all goodness there is an equal opposite, however.
Free weights require practice and maybe assistance from a professional.
Try the exercise first without weight or very little so the body learns the motion. One should be moderately strong and healthy before picking up much weight. Form is much more important and you must have some core strength to progress correctly with free weight. Injury is more likely than with machines. As in any exercise, lifting free weights has limitations.