My first job interview, what should I do?

I've got my first job interview for a summer job as a camp counsellor. I was told when I got the call today that I would be interviewed "panel style", so what does that mean? Also, I'm a teenage boy so should I sort of dress up for it? They said that it would be a plus if I had first aid but I don't. So basically I was wondering if you have any suggestions on what I should do, or any interview questions that I might recieve for this type of job and also, what do I do and how should I act at a panel style job interview. Thanks to all who add input (: