When they made me see one, it was a bunch of questionnaires about my mood, my psychotic state, some kind of 'danger to self or others' assessment. They took a medical history and did some very basic medical tests - like they took my blood pressure. They asked a few questions about whether I smoke, drink or take illicit drugs. Then they asked me a bunch of questions about how I spend my days and what I like to do and what I find stressful.
And you can tell them about your voices or not, as you please. Remember, they can't make you take drugs if you don't want them and you're not trying to hurt anybody -- so it should be 'safe' to tell.