What is the difference between microwave and convection microwave combo?
Most of this has been asked and answered, just not all together in one place.  See:


What are the pros and cons of Convection Microwave Ovens?
Is it wise to use an aluminum foil in the microwave? Is there a substitute for the aluminum foil?
Why is some metal safe to use in a microwave, but others not?


The combination oven by its very nature has a two different cooking modes:  microwave, and conventional heating.  Some can do both at the same time, to speed cooking while mitigating the disadvantages (no browning or crisping) of microwave cookery.

The mode you choose to use when reheating food will determine  how it gets reheated.  Some foods are best done by microwave (such as soups, stews, braises, saucy curries), and some by conventional cooking (fried foods, some breads or toast).  This is not to say there is an ideal way to reheat everything:  some foods (like pizza or deep fried foods) are notoriously difficult to reheat well.