Google and Bing have automated programs that read the entire Internet and capture what is out there. These programs are called crawlers.
It works like this: Say you write a new article on HubPages. After 24 hours, HubPages opens it up to the crawlers. The crawlers read it and feed the Google and Bing indexing engines. After that, anyone in the world who searches on Google or Bing for a word that is important in your article will find your page - somewhere in the listing.
If you edit your article, it will get crawled again, sooner or later.