They will watch you, listen to you, but most importantly they will feel the energy you convey. Confidence, positivity, and demeanor is important here. They know what you can do - it's on the resume. The interview is to exceed the expectation of the panel of interviewers so when they leave the interview and they reconvene to debrief, they say "how did you feel about him/her?" See? They have a feeling about you and they haven't even discussed the information of which you spoke.