Websites nowadays mostly gear towards getting high traffic volume. This is because the more people visit their site, the higher the possibility of generating income. This is especially true to sites that belong to the buy and sell category and to those who offer various kinds of services through the Internet.
Paid advertisements could increase traffic volume towards a site but another way to do it would be through search engines. Use of search engines is the primary method of web navigation for almost all Internet users. To get high rankings on search engine result listing means more chances of getting visited by web surfers. Now that majority of web traffic is directed by major search engines such as Yahoo! and Google, you would want your site to be found by search engines and your content be put into their databases so that it could be easily made available to Internet users.
On a quick note, SEO is about improving traffic site from a search engine towards a particular website via search results. This is done by making a sites content and design accessible and easier to be indexed by search engine crawlers.
There are many ways on how to optimize a site...