Generic flue dampers are fitted inside the first length of flue pipe going into the top of of your stove, or the first length going into a tee at the back of the stove. The flue damper is used to regulate the airflow to the stove making it more controllable.
These flue dampers are fitted by drilling two appropriately sized holes in the flue pipe on opposite sides. The circular plate of the flue damper is then held up inside the flue pipe, whilst the bar that lets you operate the damper is pushed through the first hole, through the plate, and then out of the other hole. Be aware that there may be sharp bits of metal from the drilling.