Microwaves heat up food. Ha just kidding!
Microwaves are lower on the spectrum. They emit less energy and have longer wavelengths. Light Waves emit more energy and have shorter wavelengths than Microwaves. Light Waves can be seen by the naked eye. Both of these waves are harmless and emit low energy, compared to waves higher in the spectrum that have smaller wavelengths, therefore more energy. Some examples are Gamma rays and X-rays, emitting high levels of energy and even radiation.
Hope that makes sense! :V