Search engines suggest the importance and the information content of a website according to their links and the keywords that the link contains for the TAG. If there are many and important links one website and another site - high-quality - so, search engines "measure" with the analysis of small programs (bots) a high link popularity. The principle is something like this: If there were two do-it-yourself stores (different websites) in one place (internet) and if a costumer would consult an adviser (search engine) to learn in which store he could buy better, so the consult would suggest the store with the most and most important costumers. So, criteria like craftsmen, VIPs etc. would be listed to "important".