A typical confusion when getting comfortable with the server is the distinction between the web server and the Communication Server. They are not the same thing nor are they accessed the same way. To compare, let's review a typical web server and how it references files, and then compare it to the Flash Communication Server.
A web server is typically accessed as http://www.myWebSite.com/.
If you have a web server installed on your workstation, you can also access it like this: http://localHost/.
Web servers are usually accessed with a web browser such as Netscape or Internet Explorer; however, Flash applications can also access a web server. Flash uses a web server to exchange static or dynamic content. The XML object, loadVariables, loadVars, getURL, NetServices, and loadMovie are some examples of Flash objects that require a web server to exchange data. Web servers return requested text or binary data to the caller using the HTTP or secure HTTPS protocol.
The Flash Communication Server is similar to a web server, but they are not the same. The most notable difference between the two servers is the protocol that is used. The Communication Server uses Macromedia's proprietary Real Time Messaging Protocol (RTMP) to handle requests. Right now, the only technology that can communicate using the protocol is Flash Player 6. You cannot access the Communication Server through a web browser.
Web servers and Communication Servers can co-exist on a single workstation or server. You can change what port numbers the Communication Server listens on by editing the conf\Server.xml file in the install folder for the Flash Communication Server. Remember to back up the configuration file before you change it!