Terminal programs were used for calling BBSes, or services like CompuServe and BIX before they had their own client apps. It controlled the modem and could handle file download or upload. That particular product is pretty rare; you should try to preserve the working disk contents.
In that time, freeware or shareware programs were widely used, so the Sierra’s Online product had an challenge at the $70 price. I’m sure they figured it would be very tech support intensive, as there was usually a steep learning curve, and the potential for high phone or online service bills.
The psuedo-GUI was probably the Tandy DeskMate interface. It gets shelf space at Radio Shack. 🙂