scheme://host.domain[:port]/path/filename
where scheme is one of:
file
a file on your local system, or a file on an anonymous ftp server
http
a file on a World Wide Web server
gopher
a file on a Gopher server
WAIS
a file on a WAIS server
The scheme can also be news or telnet, but these are used much less often than the above. The port number can generally be omitted from the URL.
Page.