The lid of the box should swing upward to open. Then cut the bottom from coat hangars-the good metal kind. Generally we use two. Our preference for heat source is charcoal since it is much more consistent that wood coals. We use a cheap tin roasting pan to place the coals in the bottom of the oven.
Similar pans are place on the racks.
Whatever you are baking is then placed in these. The bottom rack will cook faster than the top. If you watch it carefully, the cooking will be quite good and consistent. We have used it for cookies as well as dinner rolls and even pizza. Monitoring the progress of your food is key.