Microwave oven waveguide configuration

Hi everybody,

I am trying to simulate a microwave oven using COMSOL, but I'm still a bit confused about configuring the waveguide. What is the difference between Transverse Electric (TE) and Transverse Magnetic (TM) mode? I know that when using Transverse Electric, the magnetic field is perpendicular to the direction of propagation, and the opposite happens when using the Transverse Magnetic mode. But what is practically happening inside the oven when using TE or TM mode? I mean how does TE or TM mode affecting the heated product?
Thank you so much in advance