How to set SYSTEM environment variables - SYANiDE-/RIST-ng GitHub Wiki
Setting SYSTEM environment variables on Windows 10 (and not far off for previous versions)
In start menu, type "Environment Variables". You want the one for SYSTEM ENVARS:
Select "Environment Variables" button:
Select PATH envar and click edit:
You should use the new and edit buttons to put your Python36 install directory and scripts folder on the path. Try to follow such that you've duplicated the following screenie, for the two highlghted entries.
After this has been performed, you should be able to call python from anywhere on the command line, so the following should work:
"python --version"