Python comes in two versions, 2.7 and 3.x, the reason for which is kind of stupid but we'll not get into that. Both versions are more or less the same with a few small differences, like some bracket use for Print statements or unicode handling. Either one will do, but be careful if you plan on switching code between the two versions. You can also start reading the free online book of Learn Python The Hard Way, which has versions for either [Python 2] and [Python 3] respectively.

IDE stands for [Integrated Developer Environment] and are the tools people use to actually write scripts. There are others such as IDLE, Notepad++, Code Blocks, Pythonwin, etc. Each have varying degree's of accessibility and i'm sure others will be along to share their preferred tools, but you could just as easily use any text editor like notepad or wordpad to write the scripts and then run them from the command line by typing "python myscript.py".

Python, and indeed most languages, come with a core set of functions such as Loops, Conditions, Variables, Arrays, etc. Libraries are used to extend these functions to perform more tasks, for example Pyglet and Pygame both feature functions for creating a window, handling key and mouse input, as well as audio playback, all features that are either not available or only have basic functions in core Python. If you plan on making audio games, both Pyglet or Pygame would be a good choice to start with. If you plan on adding TTS functions you can look into the Tolk, Accessible Output, or Pyttsx libraries. For advanced audio there's libaudioverse, PyAL, or some scripts I have that extend Pyglets OpenAL functionality.

Cross platform capabilities largely depend on the libraries you choose to use, most of the ones i've mentioned are already fully cross platform though, libaudioverse doesn't have mac support just yet and Accessible Ouput is windows only.

Sorry for double posting, but if I were to make an audiogame that uses jaws or NVDA or some kind of screen reader support, would I need a different library for that like one with advanced audio functions?

@magurp244
accessible_output2 works just fine on os X

Ok so on windows, if you hit f2, you can changethe filepath to, say, My game.py. How do you do that on os10? Rename in the shortcut menu just changes the title of the file, and the where pop up button only shows real text document, microsoft word or a few other ones but not python. Is there something I need to install? Or itS text edit not the right editer for this?

to rename a file in MacOS finder press enter on it. I think you can also press VO+shift+m (right click) and there is a rename option. If you are already in the terminal, you can use the mv command.
e.g:
mv my_file.txt my_file.py
also the touch command creates files for you as long as they are text based. I'm not 100% sure on all of the specifics, so if anyone could explain that better feel free. the command is:
touch file1.py file2.py file3.py
you can give as many args to the touch command as you wish and it will create the files.

@Rory, you can't change the file path with rename on windows or Linux either. The only way you can do this is via symlinks or by moving or copying the file. To change the file path, either symlink it (ln on mac and Linux, mklink on windows), move it (mv on Mac and Linux, move on Windows) or copy (cp on Mac and Linux, copy on Windows) the file.