Contact the Oxford Colleges Admissions Office for further details. Once here for interview, the important thing is to relax and try and enjoy yourself. Interviews can be quite nerveracking and everyone feels that everybody else is much more intelligent than they are. Just remember that this is not true and that the other candidates will be just as nervous as you, however composed they may seem. You'll always find other candidates glad to talk to someone, and the current students will be on hand to chat to and answer any questions.
Most people enjoy their few days in Oxford and make lasting friendships in the process.
This may all seem a little confusing, but don't hesitate to get in touch with either the Balliol Tutor for Admissions or the JCR Admissions Officer who will help clarify things in any way they can. These enquiries will not in any way influence your application. Addresses, telephone numbers and e-mail addresses are at the back of the prospectus.