A regular oven provides heat from a heating element (which may be gas, electric, wood fuel etc), which heats the air in the oven. A microwave provides heat by using radiowaves to agitate responsive molecules (water is one) in the food - any warmth you feel when opening a microwave has come from heating the food, not the microwave itself.

When metal is in a microwave, the radiowaves hitting the metal create sparks, and sparks kill electronics.