Django has many management commands. In addition, we can write our own commands.
What happens after I make a shell call python manage.py XXX?
Will the code be executed in a process that launched from the shell?
Or the shell process just communicates with the main Django process that executes the command?
The shell starts a new process to run the Python interpreter. The Python interpreter reads manage.py and executes it directly. There's no such thing as "the main Django process".