SEO is adding the correct words to a website so that the right results are returned by a search engine. If you are looking for a chemist for example, you would type into Google or Bing something like:
Chemist, pharmacy, Portsmouth (or your local town) PO5 4DF (or your local post code).
This is known as local search. In your website we would place text and code that will enable Google or Bing to place your page on the first page for the keyword or keyword phrase that you want to be found.