Search Engine Optimisation (SEO) is the process of improving the visibility of a web site or web page in search engines via the natural or unpaid (Organic) search results. (Wikipedia)
Other forms include search engine marketing or paid listings such as Google Adwords.
Search Engine Optimisation only affects the ORGANIC search results. The Organic search will show up as shown below while paid listings will show up either on the top and or left hand side of a search page.
Search engines such as Google, Yahoo all have specific ways of looking at a websites and working out how to rank them. Good SEO is all about helping the search engines finding the information they need to help you rank higher.
There are many web companies that promise top ranking and submitting your website to hundreds or thousands of search engines but don’t believe it. There are only a few that matter so save your money. The best way of achieving a high ranking is good design, good SEO and most importantly, good content.
The other way to get on page one is to pay. Using Google Adwords can promote you to page one of a Google search but this will cost you so you have to work out if this is right for you. A good website design with good content will not need to be advertised. It will sell itself.