Typically browsers these days do not require you to type http:// as NogginBoink pointed out.
So say you have to go to microsoft's web site, you could type one of the following:
1.
http://www.microsoft.com
2.
www.microsoft.com
3. microsoft.com (this only works if the web site supports it).
One more thing, I believe outlook and word, and other similar programs rely on http:// or www in front of them to turn them into a clickable hyperlink.
www.microsoft.com or any other for that matter, is generally a host name or the name of a machine owned by the web site (you probably already know some/all of this!).