Have you ever come across a web site using a search engine and when you click on it you don't find anything?  There are ways to back track and possibly find the new location of the materials you are looking for.  

Click below for an example:
 http://www.k12science.org/tutorials/domain.html 

This could be a really great web page so you might want to know what the main site looks like or who the owner is.

A forward slash / is the equivalent of a directory. The main site in the example above is www.k12science.org which is the root directory where all other web pages and directories stem from. 

If you would like to know what is in each higher level directory, simply delete everything before the first / in your browser and hit enter. 

You will either get a web page or if the directory does not have an index page (index.html or index.htm) than a listing of all the directories files will be shown. Some sites don't like people to do that so you might find yourself being redirected to another page.

If you type in an non-existent directory for a site you will receive an error message in your browser or a custom error page, where a site operator know that people type in the wrong directory often and has designed custom pages to tell you that you are not supposed to be there.