Ken,
A convection oven is nothing more than a regular oven with a fan to circulate the heat! it's thats simple. On my unit, it is a heating element and fan intregrated into the back of the regular microwave. There is no radiation used in a convection oven.
The setting control the function: microwave only, convection only, combo bake which is 10% micro+convection and combo roast 40% micro+convection. Actual nothing more than a toaster oven with convection(FAN) & a microwave.
I don't ever remember seeing a Combo unit in a house, only in motorhomes. Infact, I'm not sure I remember anyone using the combo setting until I explained it to them.
I have seen convection ovens in a house's that have buttons for bake convection & roast convection. The difference is that bake convection only uses the lower element & roast uses the upper & lower element together with the fan.
Baking in the combo mode takes a little learning as it is more delicate, but as you can see I've mastered at least these 2 items