Hi Rooter, a barometric damper senses the draft in the flue pipe, and once the draft exceeds the force needed to open the flapper on the baro-damper, the draft will not exceed what it takes to open the flapper.. The force needed to open the flapper is adjustable with a sliding weight..
A baro damper only functions to limit the maximum draft.. This way if the wind starts to really blow, or the temperature plummets overnight, or both, the excess draft created won't pull too much air though your fire, burning the coal to fast, and possibly overfiring your stove.. The draft will be limited by the baro-damper.
There are several topics in the forums about Barometric Dampers.. Since you are new at burning coal,, I'd recommend reading the fourm some:
about startting a fire in a hand-fired stove : How to Light a Hand Fired Coal Stove
about chimneys and Baro Dampers: Baro damper?
reading about maintaining a good fire..
This will give you a good education base to start with for your first burn and first few weeks of heating with coal... you will quickly learn 'the ropes'.
Hope this helps.. Greg L