Marketing and sales always have been a close relationship, so close in fact that many have confused the two as being the same. Marketing is the method of bringing customers to your business as well as making others aware of your business, product, and brand. Sales is selling the product your company offers. Sales can be achieved via phone interaction (800 sales line), web (landing page, order page), or in person (salesman).
If I could explain the relationship in the most basic of terms, I would use a Marine sniper as an example. Marketing would be the spotter while the sniper would be the sales.