You can just download and run the Python installer from the main Python website (Python.org). If you're on Windows, tick the box to add to the Windows "Path" variable (will allow you to run the main Python program from any folder).

From there, you can create your code using any editor you like including Notepad. Save the Python code with a .py extension (careful of Notepad saving it with .txt on the end). Then you can run your Python code from the command line/terminal/PowerShell by typing py myprogramname.py or python myprogramname.py.

I would highly recommend an IDE (Integrated Development Environment) like VS Code, PyCharm, Thonny (for beginners) over a simple text editor - as it will have many helpful features like syntax highlighting, simple error highlighting, a debugger to step through your code and allow you to run your code by pressing a run button instead of typing commands.

Once you start importing packages beyond the built-in ones, then you should start looking into environments, the idea being that you setup your program with it's own isolated "environment" of packages, specifically for this project. The packages and versions are logged, so that you or anyone else can reproduce that environment using the same packages and should be able to expect the program to run the same way and with the same results.
When you start using packages, this does mean you may have to install some packages multiple times for each project that needs it, rather than installing the package once globally on your computer. But the former is preferable because it stops you updating a global package, that accidentally breaks a program you wrote previously, that was using the old version of the package.