What is it that you do not understand? The page you reference provides
absolutely explicit instructions.
Is there anything unclear on this page?
www.qubes-os.org/doc/software-update-vm/
You should install software in to a templateVM, and then it will be
available in all qubes based on that template.
So choose your template - Debian or Fedora.
Download the code for the Template you chose , as instructed on that page.
Then copy the downloaded file to your template.
Run the appropriate command(s) in the template.
Shut down the template.
Start a qube based on the template and check that "code" works.