when i tell my collegs how it works, i told them first, that a main Programm only can work from the top , step for step, down to the end and start again.
so if there is anythink happend in the time you need some prozess that can work without the main program, so as a single programm in the background.
after that your scentence make more sense for your guys and girls.
Just draw some basic block-diagram with a process being done with a thread vs a subprogram call.
Then make it run (both versions) and let them see the difference.
For beginners in programming is quite hard to understand some concepts (specially if they don’t have a background in something similar either) but they catch up quite fast with visual examples.