Mac OS X 10.4 comes with Python 2.3 pre-installed by Apple. However, you are encouraged to install the most recent version of Python from the Python website (http://www.python.org). A ``universal binary'' build of Python 2.5, which runs natively on the Mac's new Intel and legacy PPC CPU's, is available there.
What you get after installing is a number of things:
The Apple-provided build of Python is installed in /System/Library/Frameworks/Python.framework and /usr/bin/python, respectively. You should never modify or delete these, as they are Apple-controlled and are used by Apple- or third-party software.
IDLE includes a help menu that allows you to access Python documentation. If you are completely new to Python you should start reading the tutorial introduction in that document.
If you are familiar with Python on other Unix platforms you should read the section on running Python scripts from the Unix shell.