How to read URLs

A URL or universal resource location appears in the address wbox of your browser. The URL for this page is pretty simple: http://small-steps.wikidot.com/htd-rurls

The protocol is http (there are others, https etc.)
The hostname is small-steps.wikidot.com
The subdomain is small-steps
The domain name is wikidot.com
The top level domain is com
The path or name of the file or document is htd-rurls

Matt Cutts has an excellent account of a more complex URL.