In undergrad I majored in Management but I took enough marketing classes that I can still summon Ries and Trout on occasion. Let's start with some basic definitions.

Sales Versus Marketing

The distinction between sales and marketing is pretty damn critical.

• Marketing is the creation of demand for a product or service
• Sales is the execution of strategies to fulfill that demand

What this means is that you do marketing BEFORE you do sales. Marketing leads to sales; not vice versa.

Advertising versus Public Relations

Advertising and Public Relations are both elements of a marketing strategy in that, when executed well, create demand. Now the best description of the difference between advertising and public relations cast them in light of traditional, male-female relationships.

• When you, the male, tell a girl how good you are in bed, that is advertising. It is inherently untrusted.
• When another girl tells the girl you're interested in how good you are in bed, that's public relations. It is generally trusted.

The rule of thumb is that if you have an advertising based strategy, you're going to have to have a lot more "impressions" or "views" of the advertising for it to have the same impact as public relations but public relations is more hands on / takes more work. Whereas with advertising you simply spend money.