python-mode.el (from https://gitlab.com/python-mode-devs/python-mode) has more "bells-and-whistles" than
python.el (included with Emacs). Things like better integration with IPython and auto-completers, integration with Pymacs (python<->elisp bindings), filling, etc. You can read for yourself its features at its gitlab.
When it's said that they work together, it's meant that they don't interfere with each other. Not that they complement each other. They're two different packages that do the same task; helping to write and work with python code.
The Emacs Wiki has an extensive page on Programming Python in Emacs that describes the two modes and other Python related packages.
As far as enabling
python-mode... if you want to use
python-mode.el then yes, you need to install and enable it. Otherwise you'll use the included
python.el. I think @Drew intended to show you how you can see which one is currently active in your Emacs. By inspecting the variable
C-h v RET auto-mode-alist you can see what mode is associated with your
*.py files. Unfortunately, it's always going to show
python-mode whether you're using
A better way to find out which version you're using is to open a python file, and in that buffer do
C-h m RET. This will give you a help window describing the major and minor modes active in the buffer. First will be a list of minor modes, then the major mode. Since you did this from a python buffer, you'll see something like:
Python mode defined in 'python.el':
Major mode for editing Python files.
The filename (in this example
'python.el') will be a link. Mouse click, or move the cursor over it and hit
RET. That will load the source file in another buffer that you can inspect at will.