Sometimes it's good to review the basic definitions of search engine optimization (SEO) and search engine marketing (SEM). The goal of SEO is to get ranked in the top ten when someone searches for a keyword or phrase on Google.com. The more places you are ranked in the top ten, the more traffic you get. This traffic is considered "organic" traffic that Google provides to your website free of charge. You will need to provide sweat equity in the form of good content and people linking to your site to get more people arriving at your site via search. The organic searches Google provides users always appear in the left hand column on Google. The top placement in purple and the column on the right are paid advertisements and this is referred to as search engine marketing or pay-per-click (PPC).
Pay-per-click advertising is advertising that is served up with searches. All impressions of the ad are free, but any clicks on the ad are charged to the client, hence pay per click. It is used by all the major search engines, Bing, Google and Yahoo to provide revenue for the search results they give you. Search engine marketing can be done by small business and multi-national corporations and the best place to get started is in Google AdWords and Microsoft AdCenter.