There are a number of different ways you can set up with wood chunks. For something being cooked for a long time you can mix 3-5 chunks in amongst your charcoal. As your coals are light and come to temperature so will your chunks, giving you an instant hit of smoke that will continue to be released as the rest of your coals catch light over the length of your cooking time.
Alternatively if you are grilling something you can simply put 1-2 chunks on top of your lit coals. Allow 5-10 minutes for them to catch and burn down. You are now ready to start cooking.
Like any ingredient less is more - you can always add but you can’t take away. Make sure you experiment to achieve your perfect amount of smoke.