You fill out an application online or in person. The department manager then calls you for an interview if they are interested. The department manager will set up an appointment time for when you can come in. You then come in for the interview. Sometimes, it is with just the manager and you, but then, his or her current administrative assistant (if they are available) will sit in on the interview with you because they can help the manager make a choice. They of course want to see if you're a good fit. The current admin assistant of course is the one to train you if he/she has agreed to do so.