Okay… here it goes…
The “http://” part specifies the Hypertext Transfer Protocol. In plain english, web pages. Other protocols are ftp, nntp, etc…
“www” is just a subdomain of the google domain. In *almost *all cases it is directed to the same as the url without the subdomain (http://google.com).
All in all, www is just a very commonly used and standard subdomain that points to the same thing as the URL without it.
protocol://subdomain.domain.tld/
Subdomains such as “mail” are commonly used to access the site’s mail server (but don’t necessarily have to be).
-bigmtnskier 
[SIZE=“1”][COLOR=“Silver”]I hope I didn’t screw anything up in there :P[/COLOR][/SIZE]
