You need to open your fireplace flue to create an efficient fire and reduce the amount of smoke and carbon dioxide in the room. The flue is essentially a channel inside the chimney the smoke is funneled through, and it's controlled by the damper -- a pair of small steel doors. These doors, located at the throat of the flue before it exits the chimney, need to be opened prior to igniting a fire.
The method of opening and closing the flue depends on the type of fireplace and how it was constructed and installed in the room. Modern fireplaces often have a handle installed above or inside the opening. You turn the handle to a vertical position to open the flue damper and back to a horizontal position to close it. The device is typically marked to indicate proper positioning. Standard built-in fireplaces sometimes require use of a long metal pole with a hooked end that you use to reach into the chimney and manually pull down the lever of the damper doors to open the flue. Stainless steel and cast iron flue dampers commonly are opened with a touch-button control system. Some dampers allow partial closing of the flue after initial volatiles in the wood are burned off. Magnetic flue thermometers fitted to the flue-pipe help determine proper position of the damper doors.