HT3477 Apple's instructions do not work for me when I try to create a Guest Network.

Question

  Here is what happens: The "Set Up a Guest Network" instructions do not work. Step 3, "Click Wireless and then select Enable Guest Network" leads me to  "Create a Wireless Network."
If I click on that, it leads me to create a substitute for my primary network, leaving  me with no second option that I can designate for users.  In other words, my "Guest Network" replaces my primary network.  Something in both the Airport Express manual, and in Apple's online Support comments does not jibe with what the Utility is asking me to do. 

Answer 1

Progress is welcome, once I fully understand what it is that I need to do.  I have several questions.  First, I guess, has to do with making the Express unit the replacement for the D-Router.   As it stands, now, I have the Express unit in the next room, where it is somewhat removed from interference. 
The D-Router has abundant Ethernet sockets to serve the computers and drives connected to one another in close proximity in the office.  The Express has one open Ethernet socket.  Therefore, I don't see how I can use the Express in lieu of the D-Router.   Do you disagree?
How would the Ethernet switch that you mentioned work with the Comcast modem and the Express?  What would I need to know about connecting them, defining them to the computer, to each other, etc.? 
Connectivity is largely a foreign language to me, so it would help to have information about guides, manuals, etc., that could walk a relative ignoramus through the process of getting them to work well together.  Can you suggest any such sources? 
Also, is there an Ethernet switch that you would recommend?