It would be great to advertisedirectlyto the people who have shown an interest in trading with you for your products and services, wouldn't it?
Well in the simplest terms that is exactly what is happening every time someone types in a keyword or key phrase into a search engine that is relevant to you and your business.
So for example if you own a shoe shop that specialises in ' Red Shoes ' you obviously want your website to be brought back at or near the top of those search results.
So when someone does a search for ' Red Shoes ' the websites selling Red Shoes will be brought back and yours will be at the top.