Search Engine Optimization (SEO) helps with getting a better ranking on search engines like Google. Think of it like internet quality control. Searches such as Google like to show interesting/ popular content first.
Google search will display links to pages that are the most relevant and also by the number of quality links from other pages. This does not mean just banners. It also means using the right keywords and tags, and linking to sites that are already high up on Google’s watchlist- like adding your twitter or facebook links, or even having a blog on your site that gets popular and tweeted by your visitors, etc.