Intern. Editorial assistant. Assistant editor. Associate editor. Etc. It's a clear path, but not one you necessarily have to take. As the examples in this Ed2010 article show, if you have experience in another field and want to get into magazines, you can. The trick is to communicate how your skills are transferable and that you "get" magazines. And perhaps your non-magazine experience is a bonus that will make you stand out among all the other applicants.