Basically you put unlit charcoal in a charcoal basket, put some lit on top & let it burn down. The amount of unlit and lit depends on the size of the cooker, how long you want to cook, etc. That's the most basic explanation. It can be done in an offset, but you make sure and put the lit coals away from the intake draft - the basic concept is you're working against the airflow in order to prolong burn time.