I had one of these! You had to load the terminal software from the included cassette tape, pick up the telephone, dial the digits (literally, we didn't have TouchTone), wait for the Bell 103 handshake tones, then quickly unplug the handset and plug the cable into the modem. Set the handset aside so you don't accidentally hang up.
Then enjoy BBSing on the 22x23 display! Good times.
I think I typed in the terminal program from the book to start. That’s the day I learned that not every computer agreed what number “a” is.
An older peer quickly set me up with a better terminal on a floppy.
tangentially related - I remember my Dad bringing home a Vic-20, pecking in a sample program and then nothing but syntax errors, despite it being entered exactly the same as the printed manual. Turns out the number 0 and the letter O are not the same thing to a computer.
I learned very quickly that computers are simultaneously really smart and really dumb. That's served me well over the years.
Considering your user name, that's not surprising! ;)