Advertising is one component of marketing – specifically, the part focused on paid promotion. Marketing is broader and includes everything from product development and pricing to branding, research, and distribution.
Think of it this way: marketing is the strategy, and advertising is one of the tactics. You can have a brilliant ad, but if your pricing is off or your target audience is unclear, it won’t perform. Advertising is important, but it works best when it’s part of a well-thought-out marketing plan.