The basic difference between these three is that advertising and sales are both aspects of marketing in general. Marketing is a term that refers to so much more than just advertising or selling. Marketing refers to the entire process of deciding what goods and services a company should make, making the products, moving them to people who will buy them, and actually exchanging the products for money. This means that marketing involves practically everything that a company does.
Advertising is one aspect of marketing. Advertising involves making potential customers aware of the goods and services that a firm has available. Advertising also involves trying to persuade potential customers that they should buy those products. However, unlike sales, advertising is not really a hands-on process. It does not involve engaging with individual clients. Instead, advertising disseminates a more generalized message to an overall target audience.
Sales is also a part of marketing. Sales is different from advertising because it involves selling directly to specific customers. Sales staff go to the individual customers and persuade them to buy. They negotiate prices with the customers. They work with their own company to make sure that the customers’ needs are being met. Sales involves much more personalized activities than advertising does.
These are the main ways in which these three business activities differ.
It might be easiest to think of these three stages in the following way:
marketing - the overall plan
Marketing is how you're going to make sure that you continue to meet the needs of your customers - while increasing your company's value at the same time. A good marketing strategy will highlight ways to increase the future customer base and overview the entire production-distribution systems.
advertising - getting the word out
Advertising uses the strategies from the marketing plan to increase awareness of a product. Advertising itself can come in many forms - tv/radio/print, sponsorship, promotion etc.
sales - closing the deal
Sales tends to be a short(er) term process than marketing. Sales are where new clients are confirmed and the product is sold on a (usually) one-to-one basis.
These three areas of interest are linked in many ways, but should not be confused, or ignored, as they are all vital components of a successful business