A good start in understanding marketing is understanding definitions of key terms.
Advertising and marketing aren’t the same thing.
Advertising is only a part of marketing. Marketing includes everything from conceiving of the product, through packaging, distribution, advertising, sales materials, etc. Any step in the process of getting a product (or service) to market and into the hands of a purchaser for their hard-earned money.
The reason marketing includes conception of product is because you can’t sell ice to Eskimos or buggy whips to anyone. We see this every day, people come to us with a product or service they want to sell. The first questions should be “Does anyone want this? Can they be gotten to want it with an advertising budget we can afford? Will enough of them pay a high enough price that enables you to sell it at a profit?”
An amazing number of business are started where the answer to all three questions is a resounding “NO!”