Flux is an operator running in your cluster that will watch outside repos and configuration files for changes. If a change is detected it will pull and re-apply the desired configuration. The difference to a classic CI/CD pipleline is that you declaratively describe the entire desired state of your system in git. Read about GitOps and flux: https://www.weave.works/technologies/gitops/
https://docs.fluxcd.io/en/latest/tutorials/get-started-helm.html
https://docs.fluxcd.io/en/1.17.1/faq.html#technical-questions