How do you make arguments in bash with python?

I've recently used django to make websites, and while making them, I found that I could enter arguments into python files. I used python manage.py <arg> and it would do the specific things that it's supposed to do. I tried looking into manage.py to see how this was possible, but there was nothing there that would allow me to customize these args. (these arguments are honestly hard for me to remember)

So, my question for everyone, is how to make my own arguments? Or how to customize them?