There is far more art than science. More alchemy than chemistry. Get some wood, matches and meat and go to it. You will learn far more by building a fire and watching the results than anyone here can tell you. That said, there are a few basic principles which many of us have learned the hard way.
Temperature is really what distinguishes barbecue from other forms of cooking with fire.
F. measured at the meat level allows tough meat to get tender without drying out. Stale or acrid smoke results in a strong, bitter and unpleasant flavor. Keep a small but active fire Maintain airflow through the smoker. Keep the upper damper open and regulate the fire with the bottom damper. Do not let the fire smolder or starve for air.