How to remote SSH into a MacOS or Linux terminal using the Termius app

Question

I have been playing with the Termius app on Android running downloaded shell scripts that I wrote, catting files and snooping inside my device's directories; among other goofy stuff.

I have seen in some tutorials that I can remote SSH into my computer's terminal and run commands into my Android's Termius as if I'm typing on my computer's keyboard. Having attempted these instructions myself, I've found they're no good (IMHO) and I couldn't make them work. Also, these tutorials have no good explanation for how I am actually SSHing using the Termius app.

The question is: How do I make it work and how does it work?