This exercise is used to strengthen the muscles of the upper body in a natural fashion.
Begin by lying on a flat bench and grasping a barbell at shoulder width; your palms should be facing up or towards your head. Next, extend the barbell straight over your chest, but do not fully extend your arms; your elbows should be bent slightly. Now, lower the barbell in an arc motion until the barbell is behind your head; you should feel a stretch in your chest muscles. Next, bring the barbell back to the starting position by going through the same arc like motion. Pause slightly at the top position and then repeat this movement until you have completed your set.
Slowly move the weight through this motion and do not allow the weight to swing; this could cause injuries to multiple muscles in your upper body.
You can use dumbbells or a cable machine for this same exercise.