You go to Customer Service and let them know you're there for an interview. They'll either have you sit there and wait for the customer service manager to bring you to the backroom, or take you to the back for your interview. The Customer Service Manager will then interview you and it's really easy. Just take each question as they come and use common sense to answer them. Be yourself. Then, if they think you're a good fit, they'll ask you if you can stay for a second interview with a higher up supervisor (which is a sign that you most likely got the job). The second interview is just like the first. The interviews are easy going and not intimidating at all, but nerves can still get to you if you over think it going into it (which happened to me, but they still hired me).
What I've learned about job interviews, is that no matter where you're applying, to not even think about it as an interview. No matter what these jobs want to hear or expect you to act like or whatever, you just have to be yourself. All it really is, is to be yourself and use your common sense and if they hire you, they hire you, if they don't, oh well. At least you tried. You don't need to stress yourself out about these jobs and interviews because it actually just makes your chances of getting the job worse because you walk into the interview nervous and all that just gets in the way. These jobs and people make things so much more complicated than it actually should be to get a job, so just be yourself and take it as it comes and as long as you try your best, you have to get lucky with a job sometime.