I like to think of it as public relations being only one of the
many tools a person can use to market their business. Marketing is
an overall composition of advertising, direct marketing, branding,
public relations, and more. Public relations falls under the
umbrella and creates a unique marketing tool, often more credible
in the mind of the consumer. Public relations tactics include press
releases, web site updates, community relations, government
relations, and more.
Marketing is about getting you to buy something. It used to be called sales or salesmanship. It is about managing your pocketbook.
Public Relations (PR) is about convincing you of something
whether you agree with it or not. It is about convincing you that
what you have or bought is a good thing to have or buy (or the
opposite) or about convincing you that what some else did is a good
thing (or not). It is about managing your heart and mind.
PR and Marketing is so important to any business that often businesses fail just because they don't understand these very simple fields. If they knew, if you knew, then any idea could be lifted off the ground - and it would be clear whether or not it will have success even before you start!