What does it take to establish an advertising agency?

I am an MBA and I want to get into advertising business. Though I have taken a full credit Promotion and Advertising course, I don't have the real work experience. I want to know the hierarchy and the key responsibilities of each employee.

before starting your own advertising agency, you should at least get some experience. start from the bottom and try learning how things are being done. you could also start getting connections to important people so that when you start on your own, you can contact them and get support.