As other answers will point out, you simply need to ensure that you
have a teletypewriter that can talk ASCII and a way to make it
communicate over a modern serial link such as RS-232 (possibly via an
adapter as used in the video), and the rest is exactly the same as
you'd do if you were using a terminal program on your Mac. (And
probably a USB serial ...
The presumption in this situation is that there is some computer out there that already has one or several modems connected to phone lines, set up to automatically answer incoming calls and establish terminal sessions on them. I'm not going to go into detail on how this is done.
Once that's in place, connecting using an Model 33 ASR is similar to ...