Search Engine Optimisation is the science of increasing the number and visitors to your website by improving its rank in search engine results.
Studies indicate that websites that show up on the first page of Google receive almost 95% of guests.
Google, Bing and Yahoo base their search results on the relevancy of the content on web pages that are included in its index of websites.
When you search for something, Google uses over 200 determining factors to deliver the most relevant search results to you.