Marketing is a longer term concept than sales and relates to forward looking strategies to understand customer needs, influence customer perceptions, and identify how a company can capitalize on that. The end result of the marketing process, and what it directly supports, is making sales easier. Marketing techniques and strategies are really based on what it takes to identify the right product mix, the prices for those products, and what needs to be communicated to target customers (via advertisement) in order to ensure successful sales.
One of the key aspects of marketing strategies is building a brand identity for what a company is selling and this varies from company to company. McDonalds obviously brands their food and advertising far differently than a luxury steakhouse would do. While sales is really the ‘push’ to buy the product once the customer is there, marketing is the ‘pull’ that gets the customer to you in the first place. When marketing is done effectively it can also make sales a far easier job for a company, as the customer can already be convinced and ready to buy by the time they actually enter your store (or website). Sales can still succeed without very effective marketing but it certainly makes the job more difficult.