Error pages are html pages that visitors to your site are taken to when something goes wrong. There are a number of things that could go wrong. The below cases are covered through the Error Pages tool:
400 - Bad Request - This error will occur when a viewers browser sends a request to the web server that it cannot understand. For example: If a user types in http://secure.mysite.com to attempt to access your secure site at https://secure.mysite.com
401 - Authorization Required - This error will occur when a user enters the wrong login information for a password protected area of your site.
403 - Forbidden - This error will occur when access has been disabled to a directory on your site (probably through Password Protect Directories)
404 - Wrong Page - This error will occur when the URL that is trying to be accessed does not exist. For example: If a viewer types in http://yoursite.com/index.html when your index page is http://yoursite.com/index.htm
500 - Internal Server Error - This error will occur when the web server cannot process a local request. This usually happens when a php or cgi script is having issues.
Why Would I Want to Make My Own Error Pages?
It is important to keep visitors coming back to your site. If they see a generic error page that they do not understand, they may leave your site thinking that it does not work, or that your site is unreliable.
For example: If a visitor comes to your site and your forums are not working properly, they may see a 500 error that looks something like:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, email@example.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
This error message would probably confuse most visitors. You may wish to show an error that is more comforting to users, such as:
Oops! There is an issue with the page you are trying to load. Sorry for the inconvenience. If you contact firstname.lastname@example.org and let them know the error code (500) and what time this message appeared, we will be able to get things back up and running shortly. Thanks for your patience!
You can even include background images, other images, different font styles, or other changes as this page is an html page.
What Are Those Weird Tags in the Pages?
You may see tags that look similar to <!--#echo var="HTTP_HOST" -->. These tags will print out information about the server on the error page. For example: The <!--#echo var="HTTP_HOST" --> tag will print out the name of the server your site is on. You can use these tags to provide the information you would like to get from a visitor who reports the error.