As Mike pointed out, it will depend on the type of advertising ad you are using. Some ads will rotate automatically, others ads require you to create the rotating part with either a template edit or add-on.
This forum would be for soccer teams in my client's district. I would be making the ads and would need to find some way to rotate them in the places they go. It would also be helpful to be able to have the ads tracked so the sponsors would know how many times their ads were viewed.