Discussing the details of your most recent position will come naturally, but an interviewer will likely touch upon the other jobs you included on your résumé. When you're asked to talk about a particular position from the past, you need to be prepared to divulge more than what's on your résumé.
Too often, job seekers are visibly shaken when probed about a job that isn't their most recent. If it was relevant enough to include on your résumé, an interviewer will assume that you learned something valuable from the experience and are confident with your contributions in that role. Before your interview, spend time thoughtfully revisiting all of the positions you've listed and consider how you would paint a picture of the work you did, beyond your daily duties.