When one of your customers makes a purchase, you purchase the product from a third-party company (the drop shipper, usually a manufacturer or wholesaler) for a lower price. This process is as simple as forwarding the order from your customer, a process that can actually be completely automated. (Remember you don't have any risk here of buying inventory because the sale has already been made).
Pay-per-click advertising is the easiest way to get traffic to a brand-new site. It has two advantages over waiting for the traffic to come to you organically. First, PPC ads show up on the search pages immediately, and second, PPC ads allow you to test different keywords, as well as headlines, prices and selling approaches. Not only do you get immediate traffic, but you can also use PPC ads to discover your best, highest-converting keywords. Then you can distribute the keywords throughout your site in your copy and code, which will help your rankings in the organic search results.