What is a masonry bake oven?

Wood fired bake ovens have some of the same attributes as masonry heaters.  They burn wood at very high temperature and store the heat in the masonry mass.
Once the oven is brought up to temperature and the coals removed, the baking can begin.  Bread dough is then placed on the heated hearth and the entrance plugged.
How is the food cooked in an masonry oven?

The bake oven cooks bread by the three methods of heat transfer, conduction, convection and radiation.
Conduction occurs with the placement of the bread onto the hearth.  Heat travels from hot to cold.
Convection currents of super heated air rotates inside the baking chamber.
Radiation is a direct heat flow.  It does not rely on direct contact or a medium to transfer the heat.  An example is standing in the sun and moving into the shade.   The masonry mass of the oven create infrared light waves that are long, penetrating, compared to an metal oven with an electrical element that has no mass. 

Is bread the only thing that can be cooked in a masonry oven?

Bread is not the only thing that can be cooked in an oven.  Pretty much anything that is cooked in kitchen oven can be cooked in a brick oven.  Some food require no fire and other require a fire to remain burning, as in pizza.