If this is your first enounter with MacPython you should check out the Introduction to MacPython section first, which should give you an idea what Python is all about and what you can expect to get when you install MacPython.
General Python documentationYou need the standard Python documentation (tutorial, reference manual, library reference) available at the documentation section of www.python.org.
If you are running MacPython-OSX 2.3 you can download the documentation and install it through the Package Manager for easy viewing with Apple Help Viewer.
There are also numerous books on Python available, a (non-exhaustive) list can be found through the community section on www.python.org.
MacPython-OSX specific documentationThe MacPython installer also installs an Apple Help Book that has some very basic information on using MacPython-OSX. To access this help open the PythonIDE and look at the Help menu.
The Apple Developer Site has complete documentation on most toolkits in MacOS, and a lot of this will also be installed on your machine when you install the Apple Developer Tools, through the Apple Help application. The translation between the C calls used in the documentation and the Python calls is usually straightforward.
Older MacPython documentationIn MacPython-OS9 you have a :Mac:Demo folder that has some documentation, some examples and more. The organization leaves something to be desired (to put it mildly:-) but it should have a lot of relevant information.
If you can read German there are some nice HowTo documents by Joerg Kantel at http://www.pythonmania.de/.
Tambien, si puede leer espanol, MacWorld Espana tiene un curso de programacion en Python sobre el Mac. Esta seria comenza en el numero de julio/agosto 1998.
And if you don't read spanish you can safely ignore the paragraph above:-)