Promotion is only a part of marketing.

The first thing you learn when studying marketing is the "four P's" of the marketing mix: product, price, place, promotion. Advertising is a subset of promotion. How applicable advertising is to your company's marketing strategy depends on your company.

I don't see much value in any broad-stroke commentary, but it's at least good to understand what marketing is and what it's composed of. Creating a product is as much about marketing as buying an ad.