What's the difference between marketing, PR, and advertising?

I’m looking into possible future careers in business and trying to become familiar with careers in marketing/marketing research, public relations, and advertising. However, they all seem so similar. What’s the differences and what kind of entry level careers can one seek right out of college?

BONUS QUESTION: What other jobs in business are available to someone with a business administration minor? I know about human resources, but what else is out there? And nothing in accounting/finance would apply to me probably, because my BA will be in Psychology with the business minor, so I probably wouldn’t get hired as an accountant.