I live in the UK so I don't know if my experiences will help but I've been to two psychiatric assessments to see if I qualified for CBT. At the first meeting
I was asked lots of questions about my problem and symptoms. Prior to the first appointment they sent me three questionnaires to fill in. These included symptoms, questions about how you are thinking/feeling etc. Your answers help them to work out if your main problem is anxiety or depression etc.
The first meeting took about an hour and a half. They do go into some personal questions but remember they are there to help you, so tell them everything no matter how silly you think it is. They will not think it's silly and won't judge you. It's natural to be nervous but they really are there to try and help you and sometimes it helps just to talk to experts who understand.
Have you got a date for your appointment? Take care and let us know how is goes.