Why use it?
Search engine marketing is helpful in a number of ways. The overriding goal is to increase the revenue by increasing the number of visitors to your web site. Additionally, the visitors must show a high conversion rate. In other words, the visitors who are directed to your web site should be those who are targeted. They look for a product on the internet, are directed to your web site and are convinced to purchase the product you offer. Although search engine spiders don't read web pages--people do--it is still important to provide enough information in the text of your web page that searchers are directed to your page for the answers they seek.
How does it work?
Search engine marketing is both very simple and as complex as you want it to be. It is simple in the sense that if you use a variety of keywords--ones that the searcher is likely to enter in a query box on your web page, the search engine spider will rate those favorably and your page will be returned as a response. However, this doesn't mean that just listing a lot of possible keywords on your page will make it rank higher than others selling the same product or service. This is where the complexity of the practice enters in. The web page must be readable and informative to the human reader as well.