Account Executive, Account Planner, Copy Writer, Media Planner - what area of advertising interests you? The Advertising Educational Foundation's Guide to Careers in Advertising is a great overview of the field and includes job titles and descriptions along with job/internship search tips.
Wonder what it like to have a career in public relations? The Public Relations Society of American created an overview of the field which includes everything from areas of public relations and necessary skills to a typical day at work and the job search. Take a look: does public relations sound interesting to you and, if so, how can you start preparing for the career today!
Marketing, advertising and public relations are often grouped together when exploring career options because there are many similarities in the careers. There are also distinct differences. Watch for these differences as you explore the careers: how are the career fields different? what makes one field more interesting to you? what more do you want to learn about the field?
Here's an article to get you started on exploring the differences.