Search engine marketing or SEM is all about driving traffic to your site. When you want to get people to come into your brick and mortar store you would put it in a good location, a place where everyone either drives by naturally or people gather for whatever reason. With the internet, your store front is your site, and it works completely the other way around. Traffic finds you not because of your location, but because your listed in the search engines.
Search engines scan every page on the web, every day, and rank sites based on an algorthm which is constantly changing. SEM or search engine marketers generally test several things out to figure out what works, what gives a site favorability in search rankings, and basically what puts a website above another in the search results. These marketers are very active in learning what works, testing over and over again, and typically apply everything they learn to their clients sites.
