New house fireplace?????

hey just bought a house and still learning the ins and outs of it. I started using the fireplace and i know where the flue is and how its used. I've noticed that their a handle/knob. it looks like a pinball machine handle like you use to pull back and shoot teh ball. when i pull it and shift it to teh right i here something move like steel. what could this be???? a insert????