Microwave energy is electro-magnetic energy (like light) that is produced at a certain frequency by either a magnetron, or klystron (tubes designed to produce microwave energy). This is the same energy emitted from radar, and used in masers, but at a specific frequency. They cause molecules in a substance to agitate, creating friction, and resultant heat.
Microwaving foods causes the moisture in the foods to heat, nd cook the foods. If a bad experience is encountered with microwaved foods, it is due to chemicals leached from the vessel that the food is cooked in, usually some types of plastic. Also, metals will attract the energy and cause electrical arcing to occur. Ceramic and glass vessels, rimmed with metal will not work with a microwave oven,
One more danger with microwaves is that water may be superheated and not boil. When the vessel containing the super-heated liquid is moved, the water can begin to boil explosively, splashing scalding water in every direction.
Microwaves are perfectly safe when used within their limitations.
Seeeeya; Chief Longwind of the North