The initial interview has no pass/fail, but you'd be advised to turn up looking tidy/smart, and prepared to talk about yourself, and what you have learned so far about the Royal Navy, its role, and the job you want to do.
The interviewing officer will write a shortish report about you that will go with your formal application, and it will be forwarded to the AIB. The report will be factual, and the interviewer makes no written judgement on your suitability.
The interviewer will be able to help you get onto POACs, before you get to AIB. You'll see the officer again before going to AIB, in preparation for AIB itself.
In the meantime use the RN website and other public sources to bone up. If you call in/ring the AFCO they will give/send you useful publications. Ships, Aircraft and Missiles of the RN and RM (CP38) may be a good start, though it's slightly out of date as it was published in 2004.