From the Python Download page, select the executable installer of Python3 suitable for you computer, x86-64 or X86.
Save it to the Downloads folder , open the folder and execute the installer executable, by double clicking on the filename.
After finishing it, open a command prompt, with administrator rights.
To test the installation give the command,
This should start python interpreter, otherwise try re-installing. Now install the Matplotlib plotting library by,
c:> pip install matplotlib
This should install Numpy and matplotlib
Start IDLE from the main menu. From the File menu of IDLE create new file. Type your program in it, save it with a .py extension and Press F5 to run it.