If you’re hosting your own site in your server (Windows Server for example) then you have to always keep it on for people to access it. But if you’re renting a webhost or a web space then there is no need for you to turn on you computer since you are to upload your site to the host site. And they are the one’s taking care of your site. Search engine has a mechanism called “spider†which crawls through sites and cached it. It is not simply putting your site on the web and the spider could crawl through it a cached it through their database. There are several factors involved in it. SEO or search engine optimization would give you a better understanding on how this search engines work.:confused
Thats about how they work. Still beyond belief exactly how top search engines like Google work, but you got the basic concept.