Continuous integration (CI) means every code change gets tested before it merges. Continuous delivery (CD) means passing builds can ship to staging or production with little manual work. GitHub Actions does both using YAML workflow files in your repo's `.github/workflows` folder.
A workflow has triggers (push, pull request, schedule), jobs (groups of steps), and steps (run a command, use an action). Push to `main` → install dependencies → run linter → run tests → build artifact. If anything fails, the PR shows a red X and you fix it before merge.
Actions marketplace has prebuilt steps — checkout code, set up Node, cache npm, deploy to AWS, post Slack messages. You compose them like Lego. Secrets store API keys safely; reference them as `${{ secrets.MY_KEY }}` never plain text in YAML.
Start minimal. One workflow that runs `npm test` on every PR is better than a fancy pipeline nobody maintains. Add deploy steps when tests are reliable. Use matrix builds to test multiple Node or Python versions in parallel.
Watch minutes if you are on a free plan — public repos get generous limits; private repos can burn minutes fast on heavy jobs. Cache dependencies, skip redundant work, and cancel outdated runs on the same PR.
GitLab CI, CircleCI, and Jenkins do similar jobs. GitHub Actions wins when your code is already on GitHub and you want zero extra accounts. The skill transfers — triggers, jobs, artifacts, secrets — even if you switch tools later.