How do I cook food in this square stone oven? I've recently become the owner of this outdoor stone oven. 



However, I am at loss how to cook in it. 

It continues up into a rather large chimney. The bottom has two furrows about a thumbs length in it. There are about 6 bricks made out of clay (I think) that I guess are supposed to be used in the bottom. 

I've tried using coals - that didn't work very well.
It's a barbecue. The firebricks in the bottom can be used to contain the charcoal in a smaller region, and/or be stacked to raise the grill. I recommend raising the grill as going by the picture, it looks like the food would be too close to the coals and burn before it cooks through. 

The chimney takes the smoke away from you quite nicely and is well worth having.