The interview has 2 parts. First window someone will check your documents then you go and wait again until called to second window where the american officer will interview you.
I found both parts very nerve racking, just because your future lies in the hands of the people interviewing you and checking your documents. However, i had nothing to hide so was honest and polite.
Make sure you bring full birth certificate as i only had the short one and this delayed my visa by about a week. Would have been so much nicer to walk away with my visa that day!