It is really only as complicated as you want to make it. Your "Public Interface" is, as the name suggests, simply going to be your connection to the outside world. Typically this will be your cellular line (unless your trying to do something fancy, like using your phone as a USB WiFi card for your non-WiFi enabled PC). Your "Private Interface" is how you are going to share your connection locally. To achieve the same functionality as WMWiFiRouter, you will need to choose your WLAN card (TNETW12511 on the Mogul) as your private interface. Then I just set my private IP as the conventional 192.168.0.1 (not totally necessary, but it keeps things simple) and hit "Start ICS."
*Note - before starting ICS, you will need to have an adhoc WiFi network already set up. Then go into your WiFi control panel and select Computer-to-Computer connections only.