You can download the standard Python package, among others, from Microsoft Store or directly from the Python project home page.

You must specify which Python version you would like to use with GS-Calc, selecting a given version in GS-Calc in the "Settings > Options > General" dialog box.

Unless you already have Windows system variables pointed to the Python installation folder, in the "Settings > Options > General" dialog box you must also specify the folder where the Python core library DLL (for example python39.dll for the selected version 3.9) file is located.