The needle valve replaces the stock regulator on the smoker. you need to remove from the smoker the supply line and the regulator (should be all one piece). Install the needle valve in place of the stock line and regulator. Attach needle valve assembly to the propane tank. On the smoker open the temp control knob to high (fully open). Make sure that the needle valve is in the closed position. Slowly open and light the burner. Use the needle valve to control the amount of fuel going to the burner. Make small adjustments as needed to get to the pit temp you want and to maintain temps. Leave the temp control on the smoker fully open use the needle valve to control the flow of fuel to the burner.
Keep in mind with a low flame at the burner wind can be an issue. So if it's windy, you need to make provisions to block the wind as much as possible. Especially around the bottom of the smoker.