When you enter the department's graduate program you will be assigned an adviser with whom you should consult regarding course selection and other questions; but you should always feel free to discuss any questions or concerns you may have with the department’s Director of Graduate Studies (DGS). You may change your adviser with the approval of the DGS. Over the course of your graduate studies you will be working closely with a range of faculty advisers, for your major fields, your dissertation, etc. The DGS will need to approve your choice of adviser(s), to make sure that you are working with the faculty member(s) most suited to your needs and interests; when the time comes, the department will also need to approve the composition of your dissertation committee and any changes thereto.
You should plan on meeting your adviser(s) frequently -- at the beginning, middle and end of each semester, at the very least. While you are still doing course work, you will need to meet with your adviser at the beginning of each semester, before registering, to discuss your plans for the semester and get his or her signature on a proposed plan of study for the semester; the signed plan should be turned in to the department office and will be kept in your file. Once you've finished your course work, you will need to meet with your dissertation adviser and other faculty regularly to discuss your research and report on your progress.