Hey Etienne,
Thanks for reaching out to us!
The example code there should give a good basis for you to build on top of – basically, what you would do is take the example code in that article, copy it, and paste it into the functions.php file of your theme.
This file should already exist, and you should be able to paste the code into somewhere near the bottom of the file without issue.
I hope this helps – let us know if it does, and if not, elaborate on what information we can provide to be more helpful! 🙂
Thank you,
George