Sit on the ground with your knees bent and your heels about a foot from your butt.

Lean slightly back without rounding your spine at all. It is really important, and difficult, to keep your back straight, but don’t let it curve.
Place your arms straight out in front of you with your hands one on top of the other. Your hands should be level with the bottom of your ribcage.
Pull your navel to your spine and twist slowly to the left. The movement is not large and comes from the ribs rotating, not from your arms swinging. Inhale through center and rotate to the right.
Benefits of russian twists

This core exercise is a good workout for the whole abdomen. It engages all the abdomen muscles.

It is not just your abdomen that is worked here. Your lower back too is strengthened due to the position of your back during the exercise.

The seated Russian twist strengthens the oblique muscles on the sides of the abdomen.

A strengthened abdominal muscle helps to prevent slouching and get a good posture. This projects confidence and trims your silhouette.