CI (Continuous Integration) means every change pushed to Git is built and tested automatically. CD (Continuous Delivery / Deployment) means a tested version goes to a test or production server automatically — or with one click.
The benefit is fast, predictable updates: the steps run the same way every time, errors show up early, and rolling back to a previous version is simple. These pipelines are often run by GitLab CI or GitHub Actions.
Example
A developer pushes a change to Git — the pipeline runs tests, builds a Docker image and updates the test server.