Chest flys are a great way to work your chest. The movement allows you to stretch your chest at a range of motion you feel comfortable with and then squeeze against the stretch allow you to move the weight effectively. Isolating your chest in this manner allows you to really focus the movement and get the most benefit from it.
Start lying back on the bench. Roll your shoulder down and back to pack them into place. Once your shoulder are set, engage your lats so you can safely fly your arms laterally to stretch your chest. Once you feel a good stretch in your chest, squeeze your pecs to move the weight back to the starting position.