I've researched this on different places, including stackoverflow, and I can't find an answer that helps me.
I'm using Windows 7, 64 bit, with Atom for 64 bit Windows. I have Python 3.6.1 installed in the directory C:\Users\Austin\Documents\Python. When I try to run a simple script to test Python in Atom, it says

'python' is not recognized as an internal or external command,
  operable program or batch file.
  [Finished in 0.083s]

I tried to run the same script in the command line, and it said the same thing. I'm new to programming, so please try to be a little patient.
In very direct terms, it means that there is no executable file named python.exe in any dictionary in your search path (which I think is the PATH environment variable on Windows).
First of all, try executing python from the installation directory.  If that works, you know that you have it installed properly, and that the problem is the search path.  If that fails, try again with the full path name, such as C:\Users\Austin\Documents\Python\python.exe.
Does that move you closer to a solution?
Why can't Python run in Atom?