What is SEO? SEO is search engine optimisation
a properly designed SEO friendly website will help generate traffic towards your website and improve search engine ranking, having a good domain name, SEO friendly URL's, internal & external web links all help too.
if you're not sure what all the hoo ha is about SEO, think about what you would type into a search engine like 'Google' or 'Bing' to find what you're looking for, SEO helps provide the results and many people ask...”can you guarantee me a #1 top ranking result on Google & other search engines?” the short answer is no!
there is no way an SEO professional or company can guarantee a #1 position for any search engine all the time...FACT! Beware of SEOs that claim to guarantee rankings, allege a "special relationship" with Google, or advertise a "priority submit" to Google
Google AdWords is a paid advertising campaign which makes your listing appear at the top or on the right of a search as a sponsored link but again their is no guarantee you will be top of this either.
it’s worth pointing out that you should be very weary of SEO companies that do offer these types of guarantees, as Google and other search engines constantly change their algorithms for searches, the variables change each time too.
search engines are constantly indexing web pages and applying relevant content for new searches, it's simply not possible to guarantee a number 1 position! even achieving a front page listing can be difficult sometimes.
read Google's view on SEO guarantees, please read a post on their official blog http://googleblog.blogspot.com/2009/07/how-to-steer-clear-of-money-scams.html and the full Google explanation of SEO