Tandoor ovens are made of clay with some sort of insulating material like concrete or mud on the outside. They are cylindrical and often curve inward toward the top like a beehive or jug to concentrate the heat. A top opening left clear to allow access and ventilation.
A fire is built in the bottom, which heats both the walls of the oven and the air inside to upwards of 900° Fahrenheit! Before cooking, the fire is allowed to die down to coals so that the temperature remains consistent while food is cooked.
Flatbreads like naan get slapped against the sides of the oven.
They adhere to the super-heated surface, cook very quickly, and are peeled off when they’re done. Meats are usually cooked on long skewers that are either inserted directly into the oven or cooked over the mouth of the oven.