Gitlab salsa debian automated package building steps

What are the complete steps for a simple hello world debian package to be build automatically on gitlab.What steps to write on dockerfile, how to create runner, steps in yml file?

At a guess, probably this would be enough to put in .gitlab-ci.yml:

  - build

  image: hello-world:latest
  stage: build

once the commits are made, the runner that is connected would then pick up the task and do what is supposed to be done. Not tested it, but should be enough to build it.