Office manager would call you asking for a time to come in and set with the manager for an interview. The manager would then tell you about what kind of sales and design work you may be doing. Depending on what publication you're working with, the manager will explain to you the type of ads being designed for it. Indesign skills is a key proponent in doing this type of work. If you aren't familiar with it, I would suggest lots of practice. They'll probably want a feel of your level of expertise in photoshop and indesign. Be truthful with it, because they'll drop you quickly if you say you're an expert in either and you can't meet expectations.