The gas goes through the tubes and you light some paper on fire in the oven.
It will slowly heat up a brick that later releases the heat.
It looks like a masonry heater.
According to Wikipedia, a masonry heater (or masonry stove, ceramic stove, tile stove) is a device for warming an interior space through radiant heating, by capturing the heat from periodic burning of fuel (usually wood), and then radiating the heat at a fairly constant temperature for a long period....In some areas of central and eastern Europe, these heaters are sometimes effectively fired using grass, straw, and hay. It is also common in eastern Europe to modify these efficient heaters so that they are connected to the gas network and are fueled with gas.