Python and most of its libraries are open source. It means that you can install it without any charges. You can download it from various platforms.
For our course you should download anaconda with latest stable version of python 3. Anaconda comes bundled with python and various vital libraries and editors. The download size is large (about 500 MB) so it may take some time to download and install.
If you have non windows based system you should visit anaconda site and choose appropriate download of anaconda for your system.
https://docs.anaconda.com/anaconda/install/windows/