The French top is a heavy steel plate made up out of concentric rings. A high-powered gas burner sits directly under the center of it. Any or all of these rings are removable, to expose pots and pans to the gas flames directly.
When all the rings are in place, the French top is very hot in the center and gradually cools off toward the edge. This plate allows the cook to quickly and easily control the temperature that the cookware is exposed to without having to adjust flame levels or have multiple burners going at the same time. The removable rings allow for sauteing and other forms of open-flame cooking.
The base of a French top gas range is sometimes used for storage and sometimes holds an oven. The oven may be a standard radiant heat model or a convection oven. Warming plates sometimes surround the cooking plate.