Initially HR will reach out if found the traditional way. If you know someone you will be led to the office manager of the corresponding team. They will then have you meet a mixture of team members ranging from Sales Service Executives and Account Executives. They pretty much vet you to see if you're personable, friendly and passionate about the world of advertising. Lastly you will meet the VPs who are available at the time. You will likely meet 6+ during your initial interview at the office.