If you are using a Raspberry Pi to follow this tutorial and you have the latest version of Raspbian, then you already have everything you need.
LinuxHowever, if you are are on some other Linux then you may need to install some stuff. Basically, all you need is is Python3, pip3 and Geany. To install these on a Debian/Ubuntu set up you just need to open a terminal window and install whatever packages you need, e.g.
sudo apt-get install python3
sudo apt-get install python3-pip
sudo apt-get install geany
WindowsIf you are using Windows you can find the installation instructions for Python and Geany here
When installing Python in Windows, you should tick the box that says "Add Python 3.x to PATH".