If you have a charcoal grill already, then the setup to use it as a smoker is relatively straightforward.
Here’s what you need:
Charcoal Grill, ideally one like a kettle grill with air vents to help control air flor and temperature
Fuel, good quality briquettes or lumpwood charcoal (Nothing with any additives or glues as they can taint the flavour of your food).
Lighter, natural wool lighters or a charcoal chimney
Thermometer, ideally one for insde the grill and one for the food, the analogue thermometers that are usually on the lid of the grill aren’t renowned for being very accurate at times, plus theyre measuring the temperature nowhere near where the food is cooking.
Water/drip tray, this is essential when doing a low and slow smoke. Prolonged exposure to heat can dry out meat, so keeping a full water pan in your smoker’s chamber will help prolong the flow of smoke while keeping both the heat and humidity inside stable
Here’s how:

Set your grill
In order to do a low and slow smoke on your grill you need to cook the food using an indirect heat source, i.e. the food isn’t placed directly above the hot coals.
To do this you need to create two zones within your grill, one side with the charcoal and the other side with the food.
Set your coals on one side of the grill and place your water pan on the other side which will end up being below the food you’re cooking. The pan will catch any juices and fat from the food. Plus, the water will absorb and release heat slowly, evening out the temperatures and adding a bit of moisture to the smoking process.

Set your charcoal
You can either chose to place a pile of coals on the one side and add a few heated coals from the chimney or you could set your fuel in a method known as the snake method which is designed for a low and consistent burn.
The Snake method for charcoal layout (briquettes work best for this), was created to aid a slow consistent burn and involves placing the briquettes in a stacked, neat row around the outside of the one half of the grill. It can either be lit with a natural lighter or a few hot coals from a kettle.

Light & Maintain Temperature
Light your coals, once the coals have taken add the wood chunks and keep the lid on until the grill comes up to the desired temperature. Adjust the temperature via the air intake on the bottom of the grill.
Once the temperature has settled, (generally for low and slow cook, the desired temperature is between 110C and 120C), add the food above the drip pan and cook until it reached its target temperature. Ideally you will be monitoring the temperature in the grill near the food and of the food itself. (Multi probe thermometers are great for this).
Adjust the vents as required to increase/reduce air flow to help regulate the temperature.
Try to not open the lid of the grill unless it’s to replenish fuel or water in the pan.