When you tell your operating system to spawn a process, you tell it the filename where the executable code exists, and then you might want to also provide some information to the program at startup, in python’s case the file with your python code.
So you’d open up your terminal app and type in something like
(except adjusted for where your python executable and python code is)
Typically it suffices to type only python (/usr/bin is likely in your PATH variable, which will be searched for what you typed), and typically you’d change directory to where your code is, leaving you with:
…ought to be the first thing anyone learns to do with a computer