1. Go to Python official website: https://www.python.org/

2. Click the "Downloads" link on the home page.

3. Choose the appropriate version of Python for your friends' operating systems. Python offers versions for Windows, macOS, and various Linux distributions.

4. Download and run the Python installer.

5. During the installation process there may be options that need to be selected such as adding Python to the system path. It is recommended to select this option to make Python globally available on the system.

6. Once installed, you can open and run the .py file either by double-clicking the file or invoking it from the command line by typing the command python filename.py (where "filename.py" is the name of your python script file is).