What does HFSS do to show E field in multi-port structure?

can anybody answer this question: if i want to view E field in multi-ports structure how hfss works, does it excite one port and then simulate the other part of the structure or s.th else happens?

HFSS -> Fields -> edit sources. You will need to define the magnitude and phase of your ports here. These are the excitations that are displayed in field plots.