That depends on what you are trying to achieve. Can you explain a bit more, please?
As for simply storing code on the FB, @Dietmar has already pointed out the GitWeb app for hosting core repositories. If, OTOH you want to run code, there may be various options. In the end, your FB is simply a Debian-based linux server that can do (almost) anything a regular Linux server can do.
Two very general suggestions:
Open an SSH shell and run your code in a screen or tmux session so it does not get terminated when the SSH connection is lost.
Use out-of-the-box FB Apps or Debian packages if this already covers your needs.
Set up a systemd service on your FB to run and supervise your process and start it automatically when the FB get (re-)booted, e. g. after a system upgrade.