The interview process depends on your connection with the university. If you know where you want to be on campus then first get work study funds from financial aid. Once you have that solidified, the give you an interview form. So you grab the form and take it to the department head where you want to work and talk to them. Ask about what they want you to do and if there will ever be time to study. However, this whole process is easier if you already know the place where you want to work and have already talked to them.