Search engine optimization is the process of improving ranking in search engine results by optimizing your website so that it is found, read, and indexed by search engines in the most effective manner possible.

There are many search engines, and Google is rated by many as the number one search engine in the world. 

Websites get about 90% of their search engine traffic direct from Google searches.

Users interested  in particular product/service/information could just enter a few words into a text box, click a search button and they will find a link to your web site. 

And you do not have to pay for it if you make your website "search engine friendly".

E.g If someone is looking for "iPhone 3G", he/she will enter this word and  search engines would show all the websites which contain word "iPhone 3G", search engine would give rank preference according to their search algorithm (which considers many factors like contents, quality, structure etc of the website)

Consider what it would be like if no one could easily find about your product/services. Potentially valuable customers never even know you are there.

Not appearing in search results is like loosing lot many potential customers. Hence the SEO is very important these days.

Rank in the search results is important, as users tend to click on the website results shown on the first page.

So the goal for the webmaster is to make a site easy to find, easy to follow, and easy to read for search spiders and live-visitors, with well written quality content and a fair number of relevant incoming links.

Aim is to get the visitors to the door of the website !

While basic SEO can be time consuming in the initial stages, the results are almost always worth it and set the stage for more advanced future work.