run .py file on Windows

[snippsat]

My Python was installed automatically (didn't know how to change directory during installation) here : C:\Users\username\AppData\Local\Programs\Python\Python36-32

You can look at this for a better path Python 3.6 and pip installation under Windows, part-2.

so where should i place the .py file?

It's up to as long as python are in environment variable Path.
Make a folder eg C:\my_py where you can have most of your files.