Heya — that can be as simple as speaking out to the stone with the intent of giving it dictation, or thinking to it. It in turn can read back or mentally 'telegraph' received messages. It's one type of such device, and, like most of Sa-Hareth, is fairly primitive. Upcoming network devices at other locations will be a bit more helpful!

At present, the stone has certain limitations as a translation and communication device, largely in terms of dialects (it can't cover the old timey native tongue of the woods' people, for instance), or purposes: it can't physically read or write for you. If Regulus were to, say, encounter a letter, he'd need to be able to sound out the characters for the device to translate them.