Server
To debug PHP scripts, PHPEdit relies on a server with PHP: You can either use PHPEdit's internal server or use your own, on your local machine or on a remote machine. Because of this client/server archictecture, when communicating with the debugger, PHPEdit needs to map the filenames using the settings you enter in the Server page:
Local root directory
This directory points to the root of your documents, by PHPEdit's point of view, meaning that PHPEdit should be able to access this path.
If your server is on the same machine (or if you use PHPEdit's internal server), you simply need to browse to it's documents root.
If it is located on a remote machine, you need to specify a network path for it's documents root, for example "\\remote_machine\share\www" or "Z:\www" if you mapped a drive to this share.
You can also specify a path relative to the project's root directory path, if all your projects use the same structure this can save you the need to configure this for every project.
Debugging using PHPEdit's internal server
PHPEdit can act as a webserver to allow quick and almost configuration less debug sessions. PHPEdit simply sends the file that are requested, and executes the php scripts using the specified PHP CGI.
You can specify any port you want, as long as it is not already used by another application.
You can then browse to documents on this server using the following syntax:
http://localhost:<port>/<document>
PHPEdit's internal server listens only for requests coming from the machine PHPEdit is running on, so you don't have to worry that your documents will be visible from outside.
The internal server is very basic and should only be used for simple debug sessions, other servers might behave differently.
Debugging using an external server
PHPEdit can use an external server for debugging, all it needs to know is the root url of your scripts.
If the external server is located on a remote machine, you also need to specify if that machine is running on Windows or not, and specify the documents root path from this machine's point of view. So for example if this machine runs under Windows this could be "C:\Program Files\Apache\htdocs", or if it is a linux machine it could be "/home/username/public_html".
Conclusion
The important thing to understand is that the local root directory , the http root url and the remote root directory all point to the same location , from different perspectives. For you debug sessions to work as expected, these paths need to be configured correctly. Of course if they are disabled in the settings dialog, they aren't needed and you don't need to bother configuring them.