A software development that plans development how developer coding and testing that process is a continuous integration and then continuous delivery is a process that auto testing on staging[docker] that will marge other code committed by other developers and then deploy to production server manually OR continuous deployment is a process that auto testing and auto-deploy to a production server, aim to automatic DevOps.
every time you do git push will trigger CI operation that will follow the user script instruction (gitlab-ci.yml) to do DevOps operation.