You create a web site for your business. If that's all you do, then it's like having a storefront in the middle of the woods. No one can find your business. The next step is to have your web site found. You can use social media and paid advertising to help people find your site, but you need to be found via the main road of the Internet and that is search.
People looking for something on the Internet generally go to search to find it. This means that your business needs to rank well in search engines. Achieving a good Internet search ranking is important to many businesses and has created its own industry called search engine optimization or SEO.
Google revolutionized Internet search and by doing, that became one of the largest companies in the world. The Google search innovation was called PageRank. Google provides a high level description of how PageRank works. "PageRank works by counting the number and quality of links to a page to determine a rough estimate of how important the website is. The underlying assumption is that more important websites are likely to receive more links from other websites."
PageRank is powerful because Google ranks almost all the pages on the web, so they can determine link quality based on many levels of links. The quality of a link is determined not just by who is linking, but the content of the site and the page and the wording of the link. This innovation greatly improved people's ability to find what they wanted on the Internet. Today most search engines use something similar to PageRank as part of their algorithm.
To improve your ranking you need to be linked to by sites that are ranked high for the key word you are trying to improve. For instance, if you were to improve your ranking for Spring Hill Restaurant you need links from a site that is recognized as having a lot of information about Spring Hill and Restaurants, say a local newspaper site. Links from a local authority will give your site a higher PageRank and move it up the search engine rankings.