I set up a similar system as yours a few weeks ago. I spent days trying to get the GUI to detect my card, as well as configure the dialplan. Don’t waste your time with the Asterisk-GUI or the FreePBX GUI; they are extremely buggy and are far from being a self contained solution to configuring your PBX. I found that hard-coding the dialplan and the feature set was much more intuitive, as the Asterisk Book can walk you through the setup process. The book is free, official, and is used by support staff themselves:
Check out the section on dialplan basics, I found it extremely helpful.
Before you begin, I would make sure that your hardware (TDM card) is working properly and configured correctly. You will need to know the “context” of each FXO modules in order to create your dialplan in extensions.conf. You can find the context for each FXO module in dahdi-channels.conf
Also note that, the Asterisk book refers to analog channels as Zap or Zaptel - replace this with dahdi.