A masonry oven is like a giant stove made out of bricks and stones. It's used to bake bread, pizza, and other yummy things.
Think of it like building a big sandcastle at the beach, but instead of using sand, you use special bricks that can handle the really hot temperatures of the oven. You stack the bricks and stones together to make a big dome-shaped oven.
Once the oven is built, you need to heat it up for a long time so it gets really hot inside. This can take hours. Then you put your bread, pizza, or whatever you're cooking inside the oven. The heat from the oven bounces around inside the dome and cooks your food really evenly.
It's kind of like a magic oven because it gets super hot and cooks things really well, and it doesn't need any electricity - just wood to make a fire. It's also really cool to look at because it's made out of bricks and stones and looks like something out of a fairy tale.