If your job is administrative, you're pretty much limited to paperwork, check-writing, or maybe hiring and firing. Administrative means having to do with overseeing the "office-y" things.
An artist doesn't have time for administrative details; they're too busy creating. A successful artist will hire a manager to handle the administrative aspects of his career, such as contacting galleries, setting up shows, and making sure they get paid for their work. People who handle administrative duties are often called bureaucrats, which is typically not a nice name to be called. Sometimes they're called "administrators." Teachers are there to teach; principals have to handle the administrative duties of running a school.